[llvm] 85b5315 - [InstSimplify] Fold abs(abs(x)) -> abs(x)

[Craig Topper via llvm-commits]

Author: Craig Topper
Date: 2020-08-01T13:25:00-07:00
New Revision: 85b5315dbe9d52766ab326e702d638fcf58579b5

URL: https://github.com/llvm/llvm-project/commit/85b5315dbe9d52766ab326e702d638fcf58579b5
DIFF: https://github.com/llvm/llvm-project/commit/85b5315dbe9d52766ab326e702d638fcf58579b5.diff

LOG: [InstSimplify] Fold abs(abs(x)) -> abs(x)

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.

Differential Revision: https://reviews.llvm.org/D85053

Added: 
    

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

Removed: 
    


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diff  --git a/llvm/lib/Analysis/InstructionSimplify.cpp b/llvm/lib/Analysis/InstructionSimplify.cpp
index d3928a502965..b1438b416d56 100644
--- a/llvm/lib/Analysis/InstructionSimplify.cpp
+++ b/llvm/lib/Analysis/InstructionSimplify.cpp
@@ -5256,6 +5256,11 @@ static Value *simplifyBinaryIntrinsic(Function *F, Value *Op0, Value *Op1,
   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 (match(Op0, m_Intrinsic<Intrinsic::abs>(m_Value(), m_Value())))
+      return Op0;
     // If the sign bit is clear already, then abs does not do anything.
     if (isKnownNonNegative(Op0, Q.DL, 0, Q.AC, Q.CxtI, Q.DT))
       return Op0;

diff  --git a/llvm/test/Transforms/InstSimplify/call.ll b/llvm/test/Transforms/InstSimplify/call.ll
index 2325dccd17a8..344cefd5b2c3 100644
--- a/llvm/test/Transforms/InstSimplify/call.ll
+++ b/llvm/test/Transforms/InstSimplify/call.ll
@@ -5,6 +5,46 @@
 declare i32 @llvm.abs.i32(i32, i1)
 declare <3 x i82> @llvm.abs.v3i82(<3 x i82>, 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
+}
+
 ; If the sign bit is known zero, the abs is not needed.
 
 define i32 @zext_abs(i31 %x) {