[PATCH] D85053: [InstSimplify] Fold abs(abs(x)) -> abs(x)

[Craig Topper via Phabricator via llvm-commits]

craig.topper created this revision.
craig.topper added reviewers: spatel, RKSimon, lebedev.ri.
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craig.topper requested review of this revision.

It's always safe to pick the earlier abs regardless of the nsw flag. We'll just lose it if it is on the outer abs but not the inner abs.


https://reviews.llvm.org/D85053

Files:
  llvm/lib/Analysis/InstructionSimplify.cpp
  llvm/test/Transforms/InstSimplify/call.ll


Index: llvm/test/Transforms/InstSimplify/call.ll
===================================================================
--- llvm/test/Transforms/InstSimplify/call.ll
+++ llvm/test/Transforms/InstSimplify/call.ll
@@ -2,6 +2,48 @@
 ; RUN: opt < %s -instsimplify -S | FileCheck %s
 ; RUN: opt < %s -passes=instsimplify -S | FileCheck %s
 
+declare i32 @llvm.abs.i32(i32, i1)
+
+define i32 @test_abs_abs_0(i32 %x) {
+; CHECK-LABEL: @test_abs_abs_0(
+; CHECK-NEXT:    [[A:%.*]] = call i32 @llvm.abs.i32(i32 [[X:%.*]], i1 false)
+; CHECK-NEXT:    ret i32 [[A]]
+;
+  %a = call i32 @llvm.abs.i32(i32 %x, i1 false)
+  %b = call i32 @llvm.abs.i32(i32 %a, i1 false)
+  ret i32 %b
+}
+
+define i32 @test_abs_abs_1(i32 %x) {
+; CHECK-LABEL: @test_abs_abs_1(
+; CHECK-NEXT:    [[A:%.*]] = call i32 @llvm.abs.i32(i32 [[X:%.*]], i1 true)
+; CHECK-NEXT:    ret i32 [[A]]
+;
+  %a = call i32 @llvm.abs.i32(i32 %x, i1 true)
+  %b = call i32 @llvm.abs.i32(i32 %a, i1 false)
+  ret i32 %b
+}
+
+define i32 @test_abs_abs_2(i32 %x) {
+; CHECK-LABEL: @test_abs_abs_2(
+; CHECK-NEXT:    [[A:%.*]] = call i32 @llvm.abs.i32(i32 [[X:%.*]], i1 false)
+; CHECK-NEXT:    ret i32 [[A]]
+;
+  %a = call i32 @llvm.abs.i32(i32 %x, i1 false)
+  %b = call i32 @llvm.abs.i32(i32 %a, i1 true)
+  ret i32 %b
+}
+
+define i32 @test_abs_abs_3(i32 %x) {
+; CHECK-LABEL: @test_abs_abs_3(
+; CHECK-NEXT:    [[A:%.*]] = call i32 @llvm.abs.i32(i32 [[X:%.*]], i1 true)
+; CHECK-NEXT:    ret i32 [[A]]
+;
+  %a = call i32 @llvm.abs.i32(i32 %x, i1 true)
+  %b = call i32 @llvm.abs.i32(i32 %a, i1 true)
+  ret i32 %b
+}
+
 declare {i8, i1} @llvm.uadd.with.overflow.i8(i8 %a, i8 %b)
 declare {i8, i1} @llvm.sadd.with.overflow.i8(i8 %a, i8 %b)
 declare {i8, i1} @llvm.usub.with.overflow.i8(i8 %a, i8 %b)
Index: llvm/lib/Analysis/InstructionSimplify.cpp
===================================================================
--- llvm/lib/Analysis/InstructionSimplify.cpp
+++ llvm/lib/Analysis/InstructionSimplify.cpp
@@ -5255,6 +5255,16 @@
   Type *ReturnType = F->getReturnType();
   unsigned BitWidth = ReturnType->getScalarSizeInBits();
   switch (IID) {
+  case Intrinsic::abs: {
+    // abs(abs(x)) -> abs(x). We don't need to worry about the nsw arg here.
+    // It is always ok to pick the earlier abs. We'll just lose nsw if its only
+    // on the outer abs.
+    if (auto *II = dyn_cast<IntrinsicInst>(Op0))
+      if (II->getIntrinsicID() == IID)
+        return II;
+
+    break;
+  }
   case Intrinsic::smax:
   case Intrinsic::smin:
   case Intrinsic::umax:


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