[PATCH] D87197: [InstSimplify] Fold degenerate abs of abs form

[Nikita Popov via Phabricator via llvm-commits]

This revision was automatically updated to reflect the committed changes.
Closed by commit rGff218cbc84ff: [InstSimplify] Fold degenerate abs of abs form (authored by nikic).

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D87197/new/

https://reviews.llvm.org/D87197

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


Index: llvm/test/Transforms/InstSimplify/abs_intrinsic.ll
===================================================================
--- llvm/test/Transforms/InstSimplify/abs_intrinsic.ll
+++ llvm/test/Transforms/InstSimplify/abs_intrinsic.ll
@@ -205,10 +205,7 @@
 define i32 @select_abs_of_abs_eq(i32 %x) {
 ; CHECK-LABEL: @select_abs_of_abs_eq(
 ; CHECK-NEXT:    [[ABS:%.*]] = call i32 @llvm.abs.i32(i32 [[X:%.*]], i1 false)
-; CHECK-NEXT:    [[NEG:%.*]] = sub i32 0, [[ABS]]
-; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i32 [[X]], 0
-; CHECK-NEXT:    [[SEL:%.*]] = select i1 [[CMP]], i32 [[NEG]], i32 [[ABS]]
-; CHECK-NEXT:    ret i32 [[SEL]]
+; CHECK-NEXT:    ret i32 [[ABS]]
 ;
   %abs = call i32 @llvm.abs.i32(i32 %x, i1 false)
   %neg = sub i32 0, %abs
@@ -220,10 +217,7 @@
 define i32 @select_abs_of_abs_ne(i32 %x) {
 ; CHECK-LABEL: @select_abs_of_abs_ne(
 ; CHECK-NEXT:    [[ABS:%.*]] = call i32 @llvm.abs.i32(i32 [[X:%.*]], i1 false)
-; CHECK-NEXT:    [[NEG:%.*]] = sub i32 0, [[ABS]]
-; CHECK-NEXT:    [[CMP:%.*]] = icmp ne i32 [[X]], 0
-; CHECK-NEXT:    [[SEL:%.*]] = select i1 [[CMP]], i32 [[ABS]], i32 [[NEG]]
-; CHECK-NEXT:    ret i32 [[SEL]]
+; CHECK-NEXT:    ret i32 [[ABS]]
 ;
   %abs = call i32 @llvm.abs.i32(i32 %x, i1 false)
   %neg = sub i32 0, %abs
@@ -236,9 +230,7 @@
 ; CHECK-LABEL: @select_nabs_of_abs_eq(
 ; CHECK-NEXT:    [[ABS:%.*]] = call i32 @llvm.abs.i32(i32 [[X:%.*]], i1 false)
 ; CHECK-NEXT:    [[NEG:%.*]] = sub i32 0, [[ABS]]
-; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i32 [[X]], 0
-; CHECK-NEXT:    [[SEL:%.*]] = select i1 [[CMP]], i32 [[ABS]], i32 [[NEG]]
-; CHECK-NEXT:    ret i32 [[SEL]]
+; CHECK-NEXT:    ret i32 [[NEG]]
 ;
   %abs = call i32 @llvm.abs.i32(i32 %x, i1 false)
   %neg = sub i32 0, %abs
@@ -251,9 +243,7 @@
 ; CHECK-LABEL: @select_nabs_of_abs_ne(
 ; CHECK-NEXT:    [[ABS:%.*]] = call i32 @llvm.abs.i32(i32 [[X:%.*]], i1 false)
 ; CHECK-NEXT:    [[NEG:%.*]] = sub i32 0, [[ABS]]
-; CHECK-NEXT:    [[CMP:%.*]] = icmp ne i32 [[X]], 0
-; CHECK-NEXT:    [[SEL:%.*]] = select i1 [[CMP]], i32 [[NEG]], i32 [[ABS]]
-; CHECK-NEXT:    ret i32 [[SEL]]
+; CHECK-NEXT:    ret i32 [[NEG]]
 ;
   %abs = call i32 @llvm.abs.i32(i32 %x, i1 false)
   %neg = sub i32 0, %abs
Index: llvm/lib/Analysis/InstructionSimplify.cpp
===================================================================
--- llvm/lib/Analysis/InstructionSimplify.cpp
+++ llvm/lib/Analysis/InstructionSimplify.cpp
@@ -3965,6 +3965,15 @@
     if (match(FalseVal, isRotate) && TrueVal == X && CmpLHS == ShAmt &&
         Pred == ICmpInst::ICMP_EQ)
       return FalseVal;
+
+    // X == 0 ? abs(X) : -abs(X) --> -abs(X)
+    // X == 0 ? -abs(X) : abs(X) --> abs(X)
+    if (match(TrueVal, m_Intrinsic<Intrinsic::abs>(m_Value(X))) &&
+        match(FalseVal, m_Neg(m_Intrinsic<Intrinsic::abs>(m_Specific(X)))))
+      return FalseVal;
+    if (match(TrueVal, m_Neg(m_Intrinsic<Intrinsic::abs>(m_Value(X)))) &&
+        match(FalseVal, m_Intrinsic<Intrinsic::abs>(m_Specific(X))))
+      return FalseVal;
   }
 
   // Check for other compares that behave like bit test.


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