[llvm] 6377464 - [InstCombine] add one-use check to cast+select narrowing transform

[Sanjay Patel via llvm-commits]

Author: Sanjay Patel
Date: 2020-07-03T11:54:09-04:00
New Revision: 63774642af1efb127c6e3eafdd44eadc54647141

URL: https://github.com/llvm/llvm-project/commit/63774642af1efb127c6e3eafdd44eadc54647141
DIFF: https://github.com/llvm/llvm-project/commit/63774642af1efb127c6e3eafdd44eadc54647141.diff

LOG: [InstCombine] add one-use check to cast+select narrowing transform

Prevent increasing the instruction count.

Added: 
    

Modified: 
    llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
    llvm/test/Transforms/InstCombine/select-bitext.ll
    llvm/test/Transforms/InstCombine/select-ctlz-to-cttz.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
index cef991a2afee..8200310afa43 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
@@ -1930,7 +1930,7 @@ Instruction *InstCombiner::foldSelectExtConst(SelectInst &Sel) {
   Type *SelType = Sel.getType();
   Constant *TruncC = ConstantExpr::getTrunc(C, SmallType);
   Constant *ExtC = ConstantExpr::getCast(ExtOpcode, TruncC, SelType);
-  if (ExtC == C) {
+  if (ExtC == C && ExtInst->hasOneUse()) {
     Value *TruncCVal = cast<Value>(TruncC);
     if (ExtInst == Sel.getFalseValue())
       std::swap(X, TruncCVal);

diff  --git a/llvm/test/Transforms/InstCombine/select-bitext.ll b/llvm/test/Transforms/InstCombine/select-bitext.ll
index d39dca940ea8..1e156e248d74 100644
--- a/llvm/test/Transforms/InstCombine/select-bitext.ll
+++ b/llvm/test/Transforms/InstCombine/select-bitext.ll
@@ -458,8 +458,7 @@ define i32 @sel_sext_const_uses(i8 %a, i8 %x) {
 ; CHECK-NEXT:    [[COND:%.*]] = icmp ugt i8 [[X:%.*]], 15
 ; CHECK-NEXT:    [[A_EXT:%.*]] = sext i8 [[A:%.*]] to i32
 ; CHECK-NEXT:    call void @use32(i32 [[A_EXT]])
-; CHECK-NEXT:    [[NARROW:%.*]] = select i1 [[COND]], i8 [[A]], i8 127
-; CHECK-NEXT:    [[R:%.*]] = sext i8 [[NARROW]] to i32
+; CHECK-NEXT:    [[R:%.*]] = select i1 [[COND]], i32 [[A_EXT]], i32 127
 ; CHECK-NEXT:    ret i32 [[R]]
 ;
   %cond = icmp ugt i8 %x, 15
@@ -474,8 +473,7 @@ define i32 @sel_zext_const_uses(i8 %a, i8 %x) {
 ; CHECK-NEXT:    [[COND:%.*]] = icmp sgt i8 [[X:%.*]], 15
 ; CHECK-NEXT:    [[A_EXT:%.*]] = zext i8 [[A:%.*]] to i32
 ; CHECK-NEXT:    call void @use32(i32 [[A_EXT]])
-; CHECK-NEXT:    [[NARROW:%.*]] = select i1 [[COND]], i8 -1, i8 [[A]]
-; CHECK-NEXT:    [[R:%.*]] = zext i8 [[NARROW]] to i32
+; CHECK-NEXT:    [[R:%.*]] = select i1 [[COND]], i32 255, i32 [[A_EXT]]
 ; CHECK-NEXT:    ret i32 [[R]]
 ;
   %cond = icmp sgt i8 %x, 15

diff  --git a/llvm/test/Transforms/InstCombine/select-ctlz-to-cttz.ll b/llvm/test/Transforms/InstCombine/select-ctlz-to-cttz.ll
index 44d284c6590a..c534acd70cdb 100644
--- a/llvm/test/Transforms/InstCombine/select-ctlz-to-cttz.ll
+++ b/llvm/test/Transforms/InstCombine/select-ctlz-to-cttz.ll
@@ -224,8 +224,7 @@ define i4 @PR45762(i3 %x4) {
 ; CHECK-NEXT:    [[T7:%.*]] = zext i3 [[T4]] to i4
 ; CHECK-NEXT:    [[ONE_HOT_16:%.*]] = shl i4 1, [[T7]]
 ; CHECK-NEXT:    [[TMP1:%.*]] = icmp eq i3 [[X4]], 0
-; CHECK-NEXT:    [[NARROW:%.*]] = select i1 [[TMP1]], i3 0, i3 [[T4]]
-; CHECK-NEXT:    [[UMUL_23:%.*]] = zext i3 [[NARROW]] to i4
+; CHECK-NEXT:    [[UMUL_23:%.*]] = select i1 [[TMP1]], i4 0, i4 [[T7]]
 ; CHECK-NEXT:    [[SEL_71:%.*]] = shl i4 [[ONE_HOT_16]], [[UMUL_23]]
 ; CHECK-NEXT:    ret i4 [[SEL_71]]
 ;