[llvm] 4af4828 - [ValueTracking] Handle non-zero ashr/lshr recurrences

[Philip Reames via llvm-commits]

Author: Philip Reames
Date: 2021-03-31T16:48:32-07:00
New Revision: 4af4828a6ef5778609c6738f674a35bc28eaf829

URL: https://github.com/llvm/llvm-project/commit/4af4828a6ef5778609c6738f674a35bc28eaf829
DIFF: https://github.com/llvm/llvm-project/commit/4af4828a6ef5778609c6738f674a35bc28eaf829.diff

LOG: [ValueTracking] Handle non-zero ashr/lshr recurrences

If we know we don't shift out bits (e.g. exact), all we need to know is that input is non-zero.

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 e5c3f3f96e3e0..cffbe927adb39 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -2237,6 +2237,9 @@ static bool isNonZeroRecurrence(const PHINode *PN) {
   case Instruction::Shl:
     return !StartC->isNullValue() &&
            (BO->hasNoUnsignedWrap() || BO->hasNoSignedWrap());
+  case Instruction::AShr:
+  case Instruction::LShr:
+    return !StartC->isNullValue() && BO->isExact();
   default:
     return false;
   }

diff  --git a/llvm/test/Analysis/ValueTracking/monotonic-phi.ll b/llvm/test/Analysis/ValueTracking/monotonic-phi.ll
index 3c2aea528cbdd..af8ad2931e10f 100644
--- a/llvm/test/Analysis/ValueTracking/monotonic-phi.ll
+++ b/llvm/test/Analysis/ValueTracking/monotonic-phi.ll
@@ -486,8 +486,7 @@ define i1 @test_lshr_exact(i8 %p, i8* %pq, i8 %n) {
 ; CHECK-NEXT:    [[CMP1:%.*]] = icmp eq i8 [[A]], [[N:%.*]]
 ; CHECK-NEXT:    br i1 [[CMP1]], label [[EXIT:%.*]], label [[LOOP]]
 ; CHECK:       exit:
-; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i8 [[A]], 0
-; CHECK-NEXT:    ret i1 [[CMP]]
+; CHECK-NEXT:    ret i1 false
 ;
 entry:
   br label %loop
@@ -561,8 +560,7 @@ define i1 @test_ashr_exact(i8 %p, i8* %pq, i8 %n) {
 ; CHECK-NEXT:    [[CMP1:%.*]] = icmp eq i8 [[A]], [[N:%.*]]
 ; CHECK-NEXT:    br i1 [[CMP1]], label [[EXIT:%.*]], label [[LOOP]]
 ; CHECK:       exit:
-; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i8 [[A]], 0
-; CHECK-NEXT:    ret i1 [[CMP]]
+; CHECK-NEXT:    ret i1 false
 ;
 entry:
   br label %loop