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[SimplifyCFG] Handle llvm.assume in passingValueIsAlwaysUndefined (#89929)
See the following example: ``` define i32 @test(i32 %cond) { entry: switch i32 %cond, label %default [ i32 0, label %case0 i32 1, label %case1 i32 2, label %case2 ] case0: br label %exit case1: br label %exit case2: br label %exit default: br label %exit exit: %bool = phi i1 [ false, %default ], [ true, %case0 ], [ true, %case1 ], [ true, %case2 ] %res = phi i32 [ 0, %default ], [ 1, %case0 ], [ 2, %case1 ], [ 3, %case2 ] call void @llvm.assume(i1 %bool) ret i32 %res } ``` The edge `%default -> %bool` is dead since it will trigger an immediate UB. Alive2: https://alive2.llvm.org/ce/z/gywJiE My benchmark shows many rust applications and some c/c++ applications (e.g., arrow/php/qemu) will benefit from this patch :)
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‎llvm/lib/Transforms/Utils/SimplifyCFG.cpp

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Original file line numberDiff line numberDiff line change
@@ -7524,6 +7524,13 @@ static bool passingValueIsAlwaysUndefined(Value *V, Instruction *I, bool PtrValu
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SI->getPointerAddressSpace())) &&
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SI->getPointerOperand() == I;
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// llvm.assume(false/undef) always triggers immediate UB.
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if (auto *Assume = dyn_cast<AssumeInst>(Use)) {
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// Ignore assume operand bundles.
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if (I == Assume->getArgOperand(0))
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return true;
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}
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if (auto *CB = dyn_cast<CallBase>(Use)) {
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if (C->isNullValue() && NullPointerIsDefined(CB->getFunction()))
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return false;

‎llvm/test/Transforms/SimplifyCFG/UnreachableEliminate.ll

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Original file line numberDiff line numberDiff line change
@@ -627,7 +627,233 @@ else:
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ret void
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}
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define i32 @test_assume_false(i32 %cond) {
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; CHECK-LABEL: @test_assume_false(
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; CHECK-NEXT: entry:
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; CHECK-NEXT: switch i32 [[COND:%.*]], label [[DEFAULT:%.*]] [
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; CHECK-NEXT: i32 0, label [[EXIT:%.*]]
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; CHECK-NEXT: i32 1, label [[CASE1:%.*]]
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; CHECK-NEXT: i32 2, label [[CASE2:%.*]]
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; CHECK-NEXT: ]
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; CHECK: case1:
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; CHECK-NEXT: br label [[EXIT]]
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; CHECK: case2:
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; CHECK-NEXT: br label [[EXIT]]
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; CHECK: default:
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; CHECK-NEXT: unreachable
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; CHECK: exit:
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; CHECK-NEXT: [[RES:%.*]] = phi i32 [ 2, [[CASE1]] ], [ 3, [[CASE2]] ], [ 1, [[ENTRY:%.*]] ]
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; CHECK-NEXT: call void @llvm.assume(i1 true)
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; CHECK-NEXT: ret i32 [[RES]]
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;
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entry:
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switch i32 %cond, label %default [
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i32 0, label %case0
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i32 1, label %case1
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i32 2, label %case2
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]
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case0:
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br label %exit
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case1:
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br label %exit
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case2:
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br label %exit
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default:
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br label %exit
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exit:
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%bool = phi i1 [ false, %default ], [ true, %case0 ], [ true, %case1 ], [ true, %case2 ]
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%res = phi i32 [ 0, %default ], [ 1, %case0 ], [ 2, %case1 ], [ 3, %case2 ]
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call void @llvm.assume(i1 %bool)
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ret i32 %res
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}
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define i32 @test_assume_undef(i32 %cond) {
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; CHECK-LABEL: @test_assume_undef(
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; CHECK-NEXT: entry:
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; CHECK-NEXT: switch i32 [[COND:%.*]], label [[DEFAULT:%.*]] [
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; CHECK-NEXT: i32 0, label [[EXIT:%.*]]
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; CHECK-NEXT: i32 1, label [[CASE1:%.*]]
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; CHECK-NEXT: i32 2, label [[CASE2:%.*]]
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; CHECK-NEXT: ]
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; CHECK: case1:
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; CHECK-NEXT: br label [[EXIT]]
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; CHECK: case2:
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; CHECK-NEXT: br label [[EXIT]]
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; CHECK: default:
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; CHECK-NEXT: unreachable
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; CHECK: exit:
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; CHECK-NEXT: [[RES:%.*]] = phi i32 [ 2, [[CASE1]] ], [ 3, [[CASE2]] ], [ 1, [[ENTRY:%.*]] ]
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; CHECK-NEXT: call void @llvm.assume(i1 true)
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; CHECK-NEXT: ret i32 [[RES]]
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;
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entry:
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switch i32 %cond, label %default [
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i32 0, label %case0
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i32 1, label %case1
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i32 2, label %case2
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]
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case0:
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br label %exit
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case1:
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br label %exit
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case2:
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br label %exit
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default:
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br label %exit
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exit:
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%bool = phi i1 [ undef, %default ], [ true, %case0 ], [ true, %case1 ], [ true, %case2 ]
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%res = phi i32 [ 0, %default ], [ 1, %case0 ], [ 2, %case1 ], [ 3, %case2 ]
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call void @llvm.assume(i1 %bool)
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ret i32 %res
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}
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define i32 @test_assume_var(i32 %cond, i1 %var) {
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; CHECK-LABEL: @test_assume_var(
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; CHECK-NEXT: entry:
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; CHECK-NEXT: switch i32 [[COND:%.*]], label [[DEFAULT:%.*]] [
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; CHECK-NEXT: i32 0, label [[EXIT:%.*]]
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; CHECK-NEXT: i32 1, label [[CASE1:%.*]]
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; CHECK-NEXT: i32 2, label [[CASE2:%.*]]
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; CHECK-NEXT: ]
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; CHECK: case1:
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; CHECK-NEXT: br label [[EXIT]]
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; CHECK: case2:
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; CHECK-NEXT: br label [[EXIT]]
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; CHECK: default:
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; CHECK-NEXT: br label [[EXIT]]
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; CHECK: exit:
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; CHECK-NEXT: [[BOOL:%.*]] = phi i1 [ [[VAR:%.*]], [[DEFAULT]] ], [ true, [[CASE1]] ], [ true, [[CASE2]] ], [ true, [[ENTRY:%.*]] ]
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; CHECK-NEXT: [[RES:%.*]] = phi i32 [ 0, [[DEFAULT]] ], [ 2, [[CASE1]] ], [ 3, [[CASE2]] ], [ 1, [[ENTRY]] ]
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; CHECK-NEXT: call void @llvm.assume(i1 [[BOOL]])
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; CHECK-NEXT: ret i32 [[RES]]
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;
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entry:
741+
switch i32 %cond, label %default [
742+
i32 0, label %case0
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i32 1, label %case1
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i32 2, label %case2
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]
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case0:
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br label %exit
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case1:
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br label %exit
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case2:
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br label %exit
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default:
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br label %exit
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exit:
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%bool = phi i1 [ %var, %default ], [ true, %case0 ], [ true, %case1 ], [ true, %case2 ]
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%res = phi i32 [ 0, %default ], [ 1, %case0 ], [ 2, %case1 ], [ 3, %case2 ]
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call void @llvm.assume(i1 %bool)
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ret i32 %res
764+
}
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define i32 @test_assume_bundle_nonnull(i32 %cond, ptr nonnull %p) {
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; CHECK-LABEL: @test_assume_bundle_nonnull(
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; CHECK-NEXT: entry:
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; CHECK-NEXT: switch i32 [[COND:%.*]], label [[DEFAULT:%.*]] [
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; CHECK-NEXT: i32 0, label [[EXIT:%.*]]
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; CHECK-NEXT: i32 1, label [[CASE1:%.*]]
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; CHECK-NEXT: i32 2, label [[CASE2:%.*]]
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; CHECK-NEXT: ]
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; CHECK: case1:
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; CHECK-NEXT: br label [[EXIT]]
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; CHECK: case2:
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; CHECK-NEXT: br label [[EXIT]]
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; CHECK: default:
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; CHECK-NEXT: br label [[EXIT]]
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; CHECK: exit:
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; CHECK-NEXT: [[PTR:%.*]] = phi ptr [ null, [[DEFAULT]] ], [ [[P:%.*]], [[CASE1]] ], [ [[P]], [[CASE2]] ], [ [[P]], [[ENTRY:%.*]] ]
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; CHECK-NEXT: [[RES:%.*]] = phi i32 [ 0, [[DEFAULT]] ], [ 2, [[CASE1]] ], [ 3, [[CASE2]] ], [ 1, [[ENTRY]] ]
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; CHECK-NEXT: call void @llvm.assume(i1 true) [ "nonnull"(ptr [[PTR]]) ]
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; CHECK-NEXT: ret i32 [[RES]]
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;
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entry:
787+
switch i32 %cond, label %default [
788+
i32 0, label %case0
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i32 1, label %case1
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i32 2, label %case2
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]
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case0:
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br label %exit
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case1:
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br label %exit
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case2:
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br label %exit
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default:
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br label %exit
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exit:
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%ptr = phi ptr [ null, %default ], [ %p, %case0 ], [ %p, %case1 ], [ %p, %case2 ]
807+
%res = phi i32 [ 0, %default ], [ 1, %case0 ], [ 2, %case1 ], [ 3, %case2 ]
808+
call void @llvm.assume(i1 true) [ "nonnull"(ptr %ptr) ]
809+
ret i32 %res
810+
}
811+
812+
define i32 @test_assume_bundle_align(i32 %cond, ptr nonnull %p) {
813+
; CHECK-LABEL: @test_assume_bundle_align(
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; CHECK-NEXT: entry:
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; CHECK-NEXT: switch i32 [[COND:%.*]], label [[DEFAULT:%.*]] [
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; CHECK-NEXT: i32 0, label [[EXIT:%.*]]
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; CHECK-NEXT: i32 1, label [[CASE1:%.*]]
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; CHECK-NEXT: i32 2, label [[CASE2:%.*]]
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; CHECK-NEXT: ]
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; CHECK: case1:
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; CHECK-NEXT: br label [[EXIT]]
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; CHECK: case2:
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; CHECK-NEXT: br label [[EXIT]]
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; CHECK: default:
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; CHECK-NEXT: br label [[EXIT]]
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; CHECK: exit:
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; CHECK-NEXT: [[PTR:%.*]] = phi ptr [ null, [[DEFAULT]] ], [ [[P:%.*]], [[CASE1]] ], [ [[P]], [[CASE2]] ], [ [[P]], [[ENTRY:%.*]] ]
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; CHECK-NEXT: [[RES:%.*]] = phi i32 [ 0, [[DEFAULT]] ], [ 2, [[CASE1]] ], [ 3, [[CASE2]] ], [ 1, [[ENTRY]] ]
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; CHECK-NEXT: call void @llvm.assume(i1 true) [ "align"(ptr [[PTR]], i32 8) ]
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; CHECK-NEXT: ret i32 [[RES]]
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;
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entry:
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switch i32 %cond, label %default [
834+
i32 0, label %case0
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i32 1, label %case1
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i32 2, label %case2
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]
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case0:
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br label %exit
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case1:
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br label %exit
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case2:
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br label %exit
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default:
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br label %exit
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exit:
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%ptr = phi ptr [ null, %default ], [ %p, %case0 ], [ %p, %case1 ], [ %p, %case2 ]
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%res = phi i32 [ 0, %default ], [ 1, %case0 ], [ 2, %case1 ], [ 3, %case2 ]
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call void @llvm.assume(i1 true) [ "align"(ptr %ptr, i32 8) ]
855+
ret i32 %res
856+
}
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632858
attributes #0 = { null_pointer_is_valid }
633859
;.

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