[PATCH] D101840: [InstSimplify] ctlz(x) -> 0 if x is known negative number

[Dávid Bolvanský via Phabricator via llvm-commits]

xbolva00 updated this revision to Diff 342757.
xbolva00 added a comment.

Generalization.


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D101840/new/

https://reviews.llvm.org/D101840

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
@@ -1469,9 +1469,7 @@
 ; CHECK-LABEL: @ctlz_sext_negative_zero_undef(
 ; CHECK-NEXT:    [[ASSUME:%.*]] = icmp slt i16 [[X:%.*]], 0
 ; CHECK-NEXT:    call void @llvm.assume(i1 [[ASSUME]])
-; CHECK-NEXT:    [[S:%.*]] = sext i16 [[X]] to i32
-; CHECK-NEXT:    [[C:%.*]] = call i32 @llvm.ctlz.i32(i32 [[S]], i1 true)
-; CHECK-NEXT:    ret i32 [[C]]
+; CHECK-NEXT:    ret i32 0
 ;
   %assume = icmp slt i16 %x, 0
   call void @llvm.assume(i1 %assume)
@@ -1480,13 +1478,35 @@
   ret i32 %c
 }
 
+define i32 @ctlz_negative_zero_undef(i32 %x) {
+; CHECK-LABEL: @ctlz_negative_zero_undef(
+; CHECK-NEXT:    [[ASSUME:%.*]] = icmp slt i32 [[X:%.*]], 0
+; CHECK-NEXT:    call void @llvm.assume(i1 [[ASSUME]])
+; CHECK-NEXT:    ret i32 0
+;
+  %assume = icmp slt i32 %x, 0
+  call void @llvm.assume(i1 %assume)
+  %c = call i32 @llvm.ctlz.i32(i32 %x, i1 true)
+  ret i32 %c
+}
+
+define i32 @ctlz_negative_zero_def(i32 %x) {
+; CHECK-LABEL: @ctlz_negative_zero_def(
+; CHECK-NEXT:    [[ASSUME:%.*]] = icmp slt i32 [[X:%.*]], 0
+; CHECK-NEXT:    call void @llvm.assume(i1 [[ASSUME]])
+; CHECK-NEXT:    ret i32 0
+;
+  %assume = icmp slt i32 %x, 0
+  call void @llvm.assume(i1 %assume)
+  %c = call i32 @llvm.ctlz.i32(i32 %x, i1 false)
+  ret i32 %c
+}
+
 define i32 @ctlz_sext_negative_zero_def(i16 %x) {
 ; CHECK-LABEL: @ctlz_sext_negative_zero_def(
 ; CHECK-NEXT:    [[ASSUME:%.*]] = icmp slt i16 [[X:%.*]], 0
 ; CHECK-NEXT:    call void @llvm.assume(i1 [[ASSUME]])
-; CHECK-NEXT:    [[S:%.*]] = sext i16 [[X]] to i32
-; CHECK-NEXT:    [[C:%.*]] = call i32 @llvm.ctlz.i32(i32 [[S]], i1 false)
-; CHECK-NEXT:    ret i32 [[C]]
+; CHECK-NEXT:    ret i32 0
 ;
   %assume = icmp slt i16 %x, 0
   call void @llvm.assume(i1 %assume)
@@ -1502,8 +1522,7 @@
 ; CHECK-NEXT:    call void @llvm.assume(i1 [[ASSUME]])
 ; CHECK-NEXT:    [[S:%.*]] = sext i16 [[X]] to i32
 ; CHECK-NEXT:    call void @use(i32 [[S]])
-; CHECK-NEXT:    [[C:%.*]] = call i32 @llvm.ctlz.i32(i32 [[S]], i1 true)
-; CHECK-NEXT:    ret i32 [[C]]
+; CHECK-NEXT:    ret i32 0
 ;
   %assume = icmp slt i16 %x, 0
   call void @llvm.assume(i1 %assume)
Index: llvm/lib/Analysis/InstructionSimplify.cpp
===================================================================
--- llvm/lib/Analysis/InstructionSimplify.cpp
+++ llvm/lib/Analysis/InstructionSimplify.cpp
@@ -5411,6 +5411,8 @@
       return X;
     if (match(Op0, m_AShr(m_Negative(), m_Value())))
       return Constant::getNullValue(ReturnType);
+    if (isKnownNegative(Op0, Q.DL, /*Depth=*/0, Q.AC, Q.CxtI, Q.DT))
+      return Constant::getNullValue(ReturnType);
     break;
   }
   case Intrinsic::smax:


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