[FuncSpec] Handle ssa_copy intrinsic calls in InstCostVisitor (#114247)

Look through ssa_copy intrinsic calls when computing codesize bonus for
a specialization.

Also remove redundant logic to skip computing codesize bonus for
ssa_copy intrinsics, now these are considered zero-cost by TTI (in PR
#75294).

Author: hazzlim

llvm/lib/Transforms/IPO/FunctionSpecialization.cpp

@@ -120,10 +120,6 @@ Cost InstCostVisitor::estimateBasicBlocks(
       continue;
 
     for (Instruction &I : *BB) {
-      // Disregard SSA copies.
-      if (auto *II = dyn_cast<IntrinsicInst>(&I))
-        if (II->getIntrinsicID() == Intrinsic::ssa_copy)
-          continue;
       // If it's a known constant we have already accounted for it.
       if (KnownConstants.contains(&I))
         continue;
@@ -402,6 +398,14 @@ Constant *InstCostVisitor::visitFreezeInst(FreezeInst &I) {
 }
 
 Constant *InstCostVisitor::visitCallBase(CallBase &I) {
+  assert(LastVisited != KnownConstants.end() && "Invalid iterator!");
+
+  // Look through calls to ssa_copy intrinsics.
+  if (auto *II = dyn_cast<IntrinsicInst>(&I);
+      II && II->getIntrinsicID() == Intrinsic::ssa_copy) {
+    return LastVisited->second;
+  }
+
   Function *F = I.getCalledFunction();
   if (!F || !canConstantFoldCallTo(&I, F))
     return nullptr;

llvm/test/Transforms/FunctionSpecialization/ssa-copy.ll

@@ -0,0 +1,113 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --include-generated-funcs --version 5
+; RUN: opt -passes=print-predicateinfo -disable-output -S < %s 2>&1 | FileCheck %s --check-prefix=PREDINF
+; RUN: opt -passes="ipsccp<func-spec>" -funcspec-min-function-size=1       \
+; RUN:                                 -funcspec-for-literal-constant=true \
+; RUN:                                 -funcspec-min-codesize-savings=50   \
+; RUN:                                 -funcspec-min-latency-savings=0     \
+; RUN:                                 -S < %s | FileCheck %s --check-prefix=FUNCSPEC
+
+; Verify that we are able to estimate the codesize savings by looking through
+; calls to ssa_copy intrinsics, which are inserted by PredicateInfo when IPSCCP
+; is run prior to FunctionSpecialization.
+define i32 @main() {
+entry:
+  %res = call i32 @test_ssa_copy(i32 0)
+  ret i32 %res
+}
+
+define i32 @test_ssa_copy(i32 %x) {
+entry:
+  br label %block1
+
+block1:
+  %cmp = icmp eq i32 %x, 0
+  br i1 %cmp, label %block2, label %exit1
+
+block2:
+  br i1 %cmp, label %block3, label %exit2
+
+block3:
+  br i1 %cmp, label %exit4, label %exit3
+
+exit1:
+  ret i32 %x
+
+exit2:
+  ret i32 %x
+
+exit3:
+  ret i32 %x
+
+exit4:
+  ret i32 999
+}
+; PREDINF-LABEL: define i32 @main() {
+; PREDINF-NEXT:  [[ENTRY:.*:]]
+; PREDINF-NEXT:    [[RES:%.*]] = call i32 @test_ssa_copy(i32 0)
+; PREDINF-NEXT:    ret i32 [[RES]]
+;
+;
+; PREDINF-LABEL: define i32 @test_ssa_copy(
+; PREDINF-SAME: i32 [[X:%.*]]) {
+; PREDINF-NEXT:  [[ENTRY:.*:]]
+; PREDINF-NEXT:    br label %[[BLOCK1:.*]]
+; PREDINF:       [[BLOCK1]]:
+; PREDINF-NEXT:    [[CMP:%.*]] = icmp eq i32 [[X]], 0
+; PREDINF:         [[CMP_0:%.*]] = call i1 @llvm.ssa.copy.i1(i1 [[CMP]])
+; PREDINF:         [[X_0:%.*]] = call i32 @llvm.ssa.copy.i32(i32 [[X]])
+; PREDINF:         [[X_4:%.*]] = call i32 @llvm.ssa.copy.i32(i32 [[X]])
+; PREDINF-NEXT:    br i1 [[CMP]], label %[[BLOCK2:.*]], label %[[EXIT1:.*]]
+; PREDINF:       [[BLOCK2]]:
+; PREDINF:         [[CMP_0_1:%.*]] = call i1 @llvm.ssa.copy.i1(i1 [[CMP_0]])
+; PREDINF:         [[X_0_1:%.*]] = call i32 @llvm.ssa.copy.i32(i32 [[X_0]])
+; PREDINF:         [[X_0_3:%.*]] = call i32 @llvm.ssa.copy.i32(i32 [[X_0]])
+; PREDINF-NEXT:    br i1 [[CMP_0]], label %[[BLOCK3:.*]], label %[[EXIT2:.*]]
+; PREDINF:       [[BLOCK3]]:
+; PREDINF:         [[X_0_1_2:%.*]] = call i32 @llvm.ssa.copy.i32(i32 [[X_0_1]])
+; PREDINF-NEXT:    br i1 [[CMP_0_1]], label %[[EXIT4:.*]], label %[[EXIT3:.*]]
+; PREDINF:       [[EXIT1]]:
+; PREDINF-NEXT:    ret i32 [[X_4]]
+; PREDINF:       [[EXIT2]]:
+; PREDINF-NEXT:    ret i32 [[X_0_3]]
+; PREDINF:       [[EXIT3]]:
+; PREDINF-NEXT:    ret i32 [[X_0_1_2]]
+; PREDINF:       [[EXIT4]]:
+; PREDINF-NEXT:    ret i32 999
+;
+;
+; FUNCSPEC-LABEL: define i32 @main() {
+; FUNCSPEC-NEXT:  [[ENTRY:.*:]]
+; FUNCSPEC-NEXT:    [[RES:%.*]] = call i32 @test_ssa_copy.specialized.1(i32 0)
+; FUNCSPEC-NEXT:    ret i32 999
+;
+;
+; FUNCSPEC-LABEL: define range(i32 1, 0) i32 @test_ssa_copy(
+; FUNCSPEC-SAME: i32 [[X:%.*]]) {
+; FUNCSPEC-NEXT:  [[ENTRY:.*:]]
+; FUNCSPEC-NEXT:    br label %[[BLOCK1:.*]]
+; FUNCSPEC:       [[BLOCK1]]:
+; FUNCSPEC-NEXT:    [[CMP:%.*]] = icmp eq i32 [[X]], 0
+; FUNCSPEC-NEXT:    br i1 [[CMP]], label %[[BLOCK2:.*]], label %[[EXIT1:.*]]
+; FUNCSPEC:       [[BLOCK2]]:
+; FUNCSPEC-NEXT:    br label %[[BLOCK3:.*]]
+; FUNCSPEC:       [[BLOCK3]]:
+; FUNCSPEC-NEXT:    br label %[[EXIT4:.*]]
+; FUNCSPEC:       [[EXIT1]]:
+; FUNCSPEC-NEXT:    ret i32 [[X]]
+; FUNCSPEC:       [[EXIT4]]:
+; FUNCSPEC-NEXT:    ret i32 999
+;
+;
+; FUNCSPEC-LABEL: define internal i32 @test_ssa_copy.specialized.1(
+; FUNCSPEC-SAME: i32 [[X:%.*]]) {
+; FUNCSPEC-NEXT:  [[ENTRY:.*:]]
+; FUNCSPEC-NEXT:    br label %[[BLOCK1:.*]]
+; FUNCSPEC:       [[BLOCK1]]:
+; FUNCSPEC-NEXT:    br label %[[BLOCK2:.*]]
+; FUNCSPEC:       [[BLOCK2]]:
+; FUNCSPEC-NEXT:    br label %[[BLOCK3:.*]]
+; FUNCSPEC:       [[BLOCK3]]:
+; FUNCSPEC-NEXT:    br label %[[EXIT4:.*]]
+; FUNCSPEC:       [[EXIT4]]:
+; FUNCSPEC-NEXT:    ret i32 poison
+;