[llvm] 5c0fb02 - [ValueTracking] Don't require non-zero step for add nuw

[Nikita Popov via llvm-commits]

Author: Nikita Popov
Date: 2021-04-14T19:06:18+02:00
New Revision: 5c0fb026c93b33dd107f6ff50723d7eed911e1ce

URL: https://github.com/llvm/llvm-project/commit/5c0fb026c93b33dd107f6ff50723d7eed911e1ce
DIFF: https://github.com/llvm/llvm-project/commit/5c0fb026c93b33dd107f6ff50723d7eed911e1ce.diff

LOG: [ValueTracking] Don't require non-zero step for add nuw

It's okay if the step is zero, we'll just stay at the same non-zero
value in that case. The valuable part of this is that the step
doesn't even need to be a constant anymore.

Added: 
    

Modified: 
    llvm/lib/Analysis/ValueTracking.cpp
    llvm/test/Analysis/ValueTracking/monotonic-phi.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index d78acdbb1cd9..c1e7cf7d1191 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -2227,11 +2227,9 @@ static bool isNonZeroRecurrence(const PHINode *PN) {
   case Instruction::Add:
     // Starting from non-zero and stepping away from zero can never wrap back
     // to zero.
-    // TODO: The constant step requirement is not needed with NUW.
-    return match(Step, m_APInt(StepC)) &&
-           ((BO->hasNoUnsignedWrap() && !StepC->isNullValue()) ||
-            (BO->hasNoSignedWrap() &&
-             StartC->isNegative() == StepC->isNegative()));
+    return BO->hasNoUnsignedWrap() ||
+           (BO->hasNoSignedWrap() && match(Step, m_APInt(StepC)) &&
+            StartC->isNegative() == StepC->isNegative());
   case Instruction::Mul:
     return match(Step, m_APInt(StepC)) &&
            ((BO->hasNoUnsignedWrap() && !StepC->isNullValue()) ||

diff  --git a/llvm/test/Analysis/ValueTracking/monotonic-phi.ll b/llvm/test/Analysis/ValueTracking/monotonic-phi.ll
index fb7865d1c323..af23450b3da9 100644
--- a/llvm/test/Analysis/ValueTracking/monotonic-phi.ll
+++ b/llvm/test/Analysis/ValueTracking/monotonic-phi.ll
@@ -88,9 +88,7 @@ define i1 @test_add_nuw_unknown_step(i8 %n, i8 %r, i8 %s) {
 ; CHECK-NEXT:    [[CMP1:%.*]] = icmp eq i8 [[A]], [[N:%.*]]
 ; CHECK-NEXT:    br i1 [[CMP1]], label [[EXIT:%.*]], label [[LOOP]]
 ; CHECK:       exit:
-; CHECK-NEXT:    [[ADD:%.*]] = or i8 [[A]], [[R:%.*]]
-; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i8 [[ADD]], 0
-; CHECK-NEXT:    ret i1 [[CMP]]
+; CHECK-NEXT:    ret i1 false
 ;
 entry:
   br label %loop