[InstCombine] Remove redundant alignment assumptions.

fhahn · fhahn · commit bfd0c02bb7fc · 2025-01-21T12:29:02.000Z
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -3226,12 +3226,13 @@ Instruction *InstCombinerImpl::visitCallInst(CallInst &CI) {
       // TODO: apply range metadata for range check patterns?
     }
 
-    // Separate storage assumptions apply to the underlying allocations, not any
-    // particular pointer within them. When evaluating the hints for AA purposes
-    // we getUnderlyingObject them; by precomputing the answers here we can
-    // avoid having to do so repeatedly there.
     for (unsigned Idx = 0; Idx < II->getNumOperandBundles(); Idx++) {
       OperandBundleUse OBU = II->getOperandBundleAt(Idx);
+
+      // Separate storage assumptions apply to the underlying allocations, not
+      // any particular pointer within them. When evaluating the hints for AA
+      // purposes we getUnderlyingObject them; by precomputing the answers here
+      // we can avoid having to do so repeatedly there.
       if (OBU.getTagName() == "separate_storage") {
         assert(OBU.Inputs.size() == 2);
         auto MaybeSimplifyHint = [&](const Use &U) {
@@ -3245,6 +3246,36 @@ Instruction *InstCombinerImpl::visitCallInst(CallInst &CI) {
         MaybeSimplifyHint(OBU.Inputs[0]);
         MaybeSimplifyHint(OBU.Inputs[1]);
       }
+
+      // Try to fold alignment assumption into a load's !align metadata, if the
+      // assumption is valid in the load's context and remove redundant ones.
+      if (OBU.getTagName() == "align" && OBU.Inputs.size() == 2) {
+        RetainedKnowledge RK = getKnowledgeFromBundle(
+            *cast<AssumeInst>(II), II->bundle_op_info_begin()[Idx]);
+        if (!RK || RK.AttrKind != Attribute::Alignment ||
+            !isPowerOf2_64(RK.ArgValue))
+          continue;
+        auto *C = dyn_cast<Constant>(RK.WasOn);
+        if (C && C->isNullValue()) {
+        } else {
+          Value *UO = getUnderlyingObject(RK.WasOn);
+          if (!UO || isa<Argument>(UO))
+            continue;
+
+          // Try to get the instruction before the assumption to use as
+          // context.
+          Instruction *CtxI = nullptr;
+          if (CtxI && II->getParent()->begin() != II->getIterator())
+            CtxI = II->getPrevNode();
+
+          auto Known = computeKnownBits(RK.WasOn, 1, CtxI);
+          unsigned KnownAlign = 1 << Known.countMinTrailingZeros();
+          if (KnownAlign < RK.ArgValue)
+            continue;
+        }
+        auto *New = CallBase::removeOperandBundle(II, OBU.getTagID());
+        return New;
+      }
     }
 
     // Convert nonnull assume like:
diff --git a/llvm/test/Transforms/InstCombine/assume-align.ll b/llvm/test/Transforms/InstCombine/assume-align.ll
@@ -1,5 +1,5 @@
 ; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --check-globals smart
-; RUN: opt -S -passes=instcombine,simplifycfg < %s 2>&1 | FileCheck %s
+; RUN: opt -S -passes='instcombine<no-verify-fixpoint>,simplifycfg' < %s 2>&1 | FileCheck %s
 
 declare void @llvm.assume(i1 noundef)
 
@@ -135,6 +135,17 @@ define ptr @fold_assume_align_pow2_of_loaded_pointer_into_align_metadata(ptr %p)
   ret ptr %p2
 }
 
+define ptr @fold_assume_align_i32_pow2_of_loaded_pointer_into_align_metadata(ptr %p) {
+; CHECK-LABEL: @fold_assume_align_i32_pow2_of_loaded_pointer_into_align_metadata(
+; CHECK-NEXT:    [[P2:%.*]] = load ptr, ptr [[P:%.*]], align 8
+; CHECK-NEXT:    call void @llvm.assume(i1 true) [ "align"(ptr [[P2]], i32 8) ]
+; CHECK-NEXT:    ret ptr [[P2]]
+;
+  %p2 = load ptr, ptr %p
+  call void @llvm.assume(i1 true) [ "align"(ptr %p2, i32 8) ]
+  ret ptr %p2
+}
+
 define ptr @dont_fold_assume_align_pow2_of_loaded_pointer_into_align_metadata_due_to_call(ptr %p) {
 ; CHECK-LABEL: @dont_fold_assume_align_pow2_of_loaded_pointer_into_align_metadata_due_to_call(
 ; CHECK-NEXT:    [[P2:%.*]] = load ptr, ptr [[P:%.*]], align 8
@@ -175,7 +186,6 @@ define ptr @dont_fold_assume_align_zero_of_loaded_pointer_into_align_metadata(pt
 define ptr @redundant_assume_align_1(ptr %p) {
 ; CHECK-LABEL: @redundant_assume_align_1(
 ; CHECK-NEXT:    [[P2:%.*]] = load ptr, ptr [[P:%.*]], align 8
-; CHECK-NEXT:    call void @llvm.assume(i1 true) [ "align"(ptr [[P2]], i32 1) ]
 ; CHECK-NEXT:    call void @foo(ptr [[P2]])
 ; CHECK-NEXT:    ret ptr [[P2]]
 ;
@@ -189,7 +199,6 @@ define ptr @redundant_assume_align_1(ptr %p) {
 define ptr @redundant_assume_align_8_via_align_metadata(ptr %p) {
 ; CHECK-LABEL: @redundant_assume_align_8_via_align_metadata(
 ; CHECK-NEXT:    [[P2:%.*]] = load ptr, ptr [[P:%.*]], align 8, !align [[META0:![0-9]+]]
-; CHECK-NEXT:    call void @llvm.assume(i1 true) [ "align"(ptr [[P2]], i32 8) ]
 ; CHECK-NEXT:    call void @foo(ptr [[P2]])
 ; CHECK-NEXT:    ret ptr [[P2]]
 ;
@@ -249,7 +258,48 @@ define ptr @redundant_assume_align_8_via_asume(ptr %p) {
   ret ptr %p
 }
 
+define void @redundant_arg_passed_to_intrinsic(ptr %dst, ptr %src) {
+; CHECK-LABEL: @redundant_arg_passed_to_intrinsic(
+; CHECK-NEXT:    call void @llvm.assume(i1 true) [ "align"(ptr [[DST:%.*]], i32 8) ]
+; CHECK-NEXT:    call void @bar()
+; CHECK-NEXT:    call void @llvm.assume(i1 true) [ "align"(ptr [[SRC:%.*]], i32 8) ]
+; CHECK-NEXT:    call void @llvm.memmove.p0.p0.i64(ptr noundef nonnull align 8 dereferenceable(16) [[DST]], ptr noundef nonnull align 8 dereferenceable(16) [[SRC]], i64 16, i1 false)
+; CHECK-NEXT:    ret void
+;
+  call void @llvm.assume(i1 true) [ "align"(ptr %dst, i32 8) ]
+  call void @bar()
+  call void @llvm.assume(i1 true) [ "align"(ptr %src, i32 8) ]
+  call void @llvm.memmove.p0.p0.i64(ptr align 8 %dst, ptr %src, i64 16, i1 false)
+  ret void
+}
+
+define void @test_store(ptr %ptr) {
+; CHECK-LABEL: @test_store(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    call void @llvm.assume(i1 true) [ "align"(ptr [[PTR:%.*]], i64 2) ]
+; CHECK-NEXT:    store i16 0, ptr [[PTR]], align 1
+; CHECK-NEXT:    ret void
+;
+entry:
+  call void @llvm.assume(i1 true) [ "align"(ptr %ptr, i64 2) ]
+  store i16 0, ptr %ptr, align 1
+  ret void
+}
+
 declare void @foo(ptr)
+declare void @bar()
+
+; !align must have a constant integer alignment.
+define ptr @dont_fold_assume_align_not_constant_of_loaded_pointer_into_align_metadata(ptr %p, i64 %align) {
+; CHECK-LABEL: @dont_fold_assume_align_not_constant_of_loaded_pointer_into_align_metadata(
+; CHECK-NEXT:    [[P2:%.*]] = load ptr, ptr [[P:%.*]], align 8
+; CHECK-NEXT:    ret ptr [[P2]]
+;
+  %p2 = load ptr, ptr %p
+  call void @llvm.assume(i1 true) [ "align"(ptr %p2, i64 %align) ]
+  ret ptr %p2
+}
+
 ;.
 ; CHECK: [[META0]] = !{i64 8}
 ;.
diff --git a/llvm/test/Transforms/InstCombine/assume.ll b/llvm/test/Transforms/InstCombine/assume.ll
@@ -1,9 +1,9 @@
 ; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
-; RUN: opt < %s -passes=instcombine -S | FileCheck --check-prefixes=CHECK,DEFAULT %s
-; RUN: opt < %s -passes=instcombine --enable-knowledge-retention -S | FileCheck --check-prefixes=CHECK,BUNDLES %s
+; RUN: opt < %s -passes='instcombine<no-verify-fixpoint>' -S | FileCheck --check-prefixes=CHECK,DEFAULT %s
+; RUN: opt < %s -passes='instcombine<no-verify-fixpoint>' --enable-knowledge-retention -S | FileCheck --check-prefixes=CHECK,BUNDLES %s
 
-; RUN: opt < %s -passes=instcombine -S --try-experimental-debuginfo-iterators | FileCheck --check-prefixes=CHECK,DEFAULT %s
-; RUN: opt < %s -passes=instcombine --enable-knowledge-retention -S --try-experimental-debuginfo-iterators | FileCheck --check-prefixes=CHECK,BUNDLES %s
+; RUN: opt < %s -passes='instcombine<no-verify-fixpoint>' -S --try-experimental-debuginfo-iterators | FileCheck --check-prefixes=CHECK,DEFAULT %s
+; RUN: opt < %s -passes='instcombine<no-verify-fixpoint>' --enable-knowledge-retention -S --try-experimental-debuginfo-iterators | FileCheck --check-prefixes=CHECK,BUNDLES %s
 
 target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
 target triple = "x86_64-unknown-linux-gnu"
