[PATCH] D59563: [ValueTracking] Compute range for abs without nsw

[Nikita Popov via Phabricator via llvm-commits]

This revision was automatically updated to reflect the committed changes.
Closed by commit rL356586: [ValueTracking] Compute range for abs without nsw (authored by nikic, committed by ).

Changed prior to commit:
  https://reviews.llvm.org/D59563?vs=191394&id=191542#toc

Repository:
  rL LLVM

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D59563/new/

https://reviews.llvm.org/D59563

Files:
  llvm/trunk/lib/Analysis/ValueTracking.cpp
  llvm/trunk/test/Transforms/InstSimplify/icmp-abs-nabs.ll


Index: llvm/trunk/test/Transforms/InstSimplify/icmp-abs-nabs.ll
===================================================================
--- llvm/trunk/test/Transforms/InstSimplify/icmp-abs-nabs.ll
+++ llvm/trunk/test/Transforms/InstSimplify/icmp-abs-nabs.ll
@@ -150,11 +150,7 @@
 ; Even if we don't have nsw, the range is still limited in the unsigned domain.
 define i1 @abs_positive_or_signed_min(i32 %x) {
 ; CHECK-LABEL: @abs_positive_or_signed_min(
-; CHECK-NEXT:    [[CMP:%.*]] = icmp slt i32 [[X:%.*]], 0
-; CHECK-NEXT:    [[NEGX:%.*]] = sub i32 0, [[X]]
-; CHECK-NEXT:    [[ABS:%.*]] = select i1 [[CMP]], i32 [[NEGX]], i32 [[X]]
-; CHECK-NEXT:    [[R:%.*]] = icmp ult i32 [[ABS]], -2147483647
-; CHECK-NEXT:    ret i1 [[R]]
+; CHECK-NEXT:    ret i1 true
 ;
   %cmp = icmp slt i32 %x, 0
   %negx = sub i32 0, %x
Index: llvm/trunk/lib/Analysis/ValueTracking.cpp
===================================================================
--- llvm/trunk/lib/Analysis/ValueTracking.cpp
+++ llvm/trunk/lib/Analysis/ValueTracking.cpp
@@ -5673,14 +5673,15 @@
 
   unsigned BitWidth = SI.getType()->getScalarSizeInBits();
 
-  // matchSelectPattern() returns the negation part of an abs pattern in RHS.
-  // If the negate has an NSW flag, abs(INT_MIN) is undefined. Without that
-  // constraint, we can't make a contiguous range for the result of abs.
-  if (R.Flavor == SelectPatternFlavor::SPF_ABS &&
-      cast<Instruction>(RHS)->hasNoSignedWrap()) {
-    // The result of abs(X) is >= 0 (with nsw).
+  if (R.Flavor == SelectPatternFlavor::SPF_ABS) {
+    // If the negation part of the abs (in RHS) has the NSW flag,
+    // then the result of abs(X) is [0..SIGNED_MAX],
+    // otherwise it is [0..SIGNED_MIN], as -SIGNED_MIN == SIGNED_MIN.
     Lower = APInt::getNullValue(BitWidth);
-    Upper = APInt::getSignedMaxValue(BitWidth) + 1;
+    if (cast<Instruction>(RHS)->hasNoSignedWrap())
+      Upper = APInt::getSignedMaxValue(BitWidth) + 1;
+    else
+      Upper = APInt::getSignedMinValue(BitWidth) + 1;
     return;
   }
 


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