[llvm] 62ce7e6 - [InstCombine] fix use check when canonicalizing abs/nabs

[Sanjay Patel via llvm-commits]

Author: Sanjay Patel
Date: 2020-02-10T14:57:37-05:00
New Revision: 62ce7e650a5a388540b5606d34bcce2fb5932498

URL: https://github.com/llvm/llvm-project/commit/62ce7e650a5a388540b5606d34bcce2fb5932498
DIFF: https://github.com/llvm/llvm-project/commit/62ce7e650a5a388540b5606d34bcce2fb5932498.diff

LOG: [InstCombine] fix use check when canonicalizing abs/nabs

We were checking for extra uses of the negated operand even
if we were not going to create it as part of this canonicalization.

This was showing up as a regression when we limit EarlyCSE as
proposed in D74285.

Added: 
    

Modified: 
    llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
    llvm/test/Transforms/InstCombine/abs-1.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
index fe47ceec4131..c086b152c09b 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
@@ -1073,10 +1073,11 @@ static Instruction *canonicalizeAbsNabs(SelectInst &Sel, ICmpInst &Cmp,
   if (CmpCanonicalized && RHSCanonicalized)
     return nullptr;
 
-  // If RHS is used by other instructions except compare and select, don't
-  // canonicalize it to not increase the instruction count.
-  if (!(RHS->hasOneUse() || (RHS->hasNUses(2) && CmpUsesNegatedOp)))
-    return nullptr;
+  // If RHS is not canonical but is used by other instructions, don't
+  // canonicalize it and potentially increase the instruction count.
+  if (!RHSCanonicalized)
+    if (!(RHS->hasOneUse() || (RHS->hasNUses(2) && CmpUsesNegatedOp)))
+      return nullptr;
 
   // Create the canonical compare: icmp slt LHS 0.
   if (!CmpCanonicalized) {

diff  --git a/llvm/test/Transforms/InstCombine/abs-1.ll b/llvm/test/Transforms/InstCombine/abs-1.ll
index f0d1fea25570..1ff8ee61cb19 100644
--- a/llvm/test/Transforms/InstCombine/abs-1.ll
+++ b/llvm/test/Transforms/InstCombine/abs-1.ll
@@ -573,8 +573,8 @@ define i8 @abs_swapped(i8 %a) {
 ; CHECK-LABEL: @abs_swapped(
 ; CHECK-NEXT:    [[NEG:%.*]] = sub i8 0, [[A:%.*]]
 ; CHECK-NEXT:    call void @extra_use(i8 [[NEG]])
-; CHECK-NEXT:    [[CMP1:%.*]] = icmp sgt i8 [[A]], 0
-; CHECK-NEXT:    [[M1:%.*]] = select i1 [[CMP1]], i8 [[A]], i8 [[NEG]]
+; CHECK-NEXT:    [[CMP1:%.*]] = icmp slt i8 [[A]], 0
+; CHECK-NEXT:    [[M1:%.*]] = select i1 [[CMP1]], i8 [[NEG]], i8 [[A]]
 ; CHECK-NEXT:    ret i8 [[M1]]
 ;
   %neg = sub i8 0, %a
@@ -588,8 +588,8 @@ define i8 @nabs_swapped(i8 %a) {
 ; CHECK-LABEL: @nabs_swapped(
 ; CHECK-NEXT:    [[NEG:%.*]] = sub i8 0, [[A:%.*]]
 ; CHECK-NEXT:    call void @extra_use(i8 [[NEG]])
-; CHECK-NEXT:    [[CMP2:%.*]] = icmp sgt i8 [[A]], 0
-; CHECK-NEXT:    [[M2:%.*]] = select i1 [[CMP2]], i8 [[NEG]], i8 [[A]]
+; CHECK-NEXT:    [[CMP2:%.*]] = icmp slt i8 [[A]], 0
+; CHECK-NEXT:    [[M2:%.*]] = select i1 [[CMP2]], i8 [[A]], i8 [[NEG]]
 ; CHECK-NEXT:    ret i8 [[M2]]
 ;
   %neg = sub i8 0, %a
@@ -603,8 +603,8 @@ define i8 @abs_
diff erent_constants(i8 %a) {
 ; CHECK-LABEL: @abs_
diff erent_constants(
 ; CHECK-NEXT:    [[NEG:%.*]] = sub i8 0, [[A:%.*]]
 ; CHECK-NEXT:    call void @extra_use(i8 [[NEG]])
-; CHECK-NEXT:    [[CMP1:%.*]] = icmp sgt i8 [[A]], -1
-; CHECK-NEXT:    [[M1:%.*]] = select i1 [[CMP1]], i8 [[A]], i8 [[NEG]]
+; CHECK-NEXT:    [[CMP1:%.*]] = icmp slt i8 [[A]], 0
+; CHECK-NEXT:    [[M1:%.*]] = select i1 [[CMP1]], i8 [[NEG]], i8 [[A]]
 ; CHECK-NEXT:    ret i8 [[M1]]
 ;
   %neg = sub i8 0, %a
@@ -618,8 +618,8 @@ define i8 @nabs_
diff erent_constants(i8 %a) {
 ; CHECK-LABEL: @nabs_
diff erent_constants(
 ; CHECK-NEXT:    [[NEG:%.*]] = sub i8 0, [[A:%.*]]
 ; CHECK-NEXT:    call void @extra_use(i8 [[NEG]])
-; CHECK-NEXT:    [[CMP2:%.*]] = icmp sgt i8 [[A]], -1
-; CHECK-NEXT:    [[M2:%.*]] = select i1 [[CMP2]], i8 [[NEG]], i8 [[A]]
+; CHECK-NEXT:    [[CMP2:%.*]] = icmp slt i8 [[A]], 0
+; CHECK-NEXT:    [[M2:%.*]] = select i1 [[CMP2]], i8 [[A]], i8 [[NEG]]
 ; CHECK-NEXT:    ret i8 [[M2]]
 ;
   %neg = sub i8 0, %a