[llvm] d69efa4 - [BasicAA] Handle disjoint or as add in DecomposeGEP. (#78209)

[via llvm-commits]

Author: David Green
Date: 2024-01-16T09:22:20Z
New Revision: d69efa4015ca41746b1aa517976cc376bce48860

URL: https://github.com/llvm/llvm-project/commit/d69efa4015ca41746b1aa517976cc376bce48860
DIFF: https://github.com/llvm/llvm-project/commit/d69efa4015ca41746b1aa517976cc376bce48860.diff

LOG: [BasicAA] Handle disjoint or as add in DecomposeGEP. (#78209)

This removes the MaskedValueIsZero check in decomposing geps in BasicAA, using
the isDisjoint flags instead. This relies on the disjoint flags being present
when AA is ran. The alternative would be to keep the old MaskedValueIsZero check
too if this causes issues.

Added: 
    

Modified: 
    llvm/lib/Analysis/BasicAliasAnalysis.cpp
    llvm/test/Analysis/BasicAA/gep-alias.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Analysis/BasicAliasAnalysis.cpp b/llvm/lib/Analysis/BasicAliasAnalysis.cpp
index a4a0846df7af155..ab1ab106659e7e7 100644
--- a/llvm/lib/Analysis/BasicAliasAnalysis.cpp
+++ b/llvm/lib/Analysis/BasicAliasAnalysis.cpp
@@ -393,10 +393,8 @@ static LinearExpression GetLinearExpression(
         // further.
         return Val;
       case Instruction::Or:
-        // X|C == X+C if all the bits in C are unset in X.  Otherwise we can't
-        // analyze it.
-        if (!MaskedValueIsZero(BOp->getOperand(0), RHSC->getValue(),
-                               SimplifyQuery(DL, DT, AC, BOp)))
+        // X|C == X+C if it is disjoint.  Otherwise we can't analyze it.
+        if (!cast<PossiblyDisjointInst>(BOp)->isDisjoint())
           return Val;
 
         [[fallthrough]];

diff  --git a/llvm/test/Analysis/BasicAA/gep-alias.ll b/llvm/test/Analysis/BasicAA/gep-alias.ll
index 302986254266419..132cc496b8f7d9e 100644
--- a/llvm/test/Analysis/BasicAA/gep-alias.ll
+++ b/llvm/test/Analysis/BasicAA/gep-alias.ll
@@ -114,7 +114,7 @@ define i32 @test5_as1_same_size(ptr addrspace(1) %p, i16 %i) {
 define i32 @test6(ptr %p, i64 %i1) {
   %i = shl i64 %i1, 2
   %pi = getelementptr i32, ptr %p, i64 %i
-  %i.next = or i64 %i, 1
+  %i.next = or disjoint i64 %i, 1
   %pi.next = getelementptr i32, ptr %p, i64 %i.next
   %x = load i32, ptr %pi
   store i32 42, ptr %pi.next
@@ -125,6 +125,21 @@ define i32 @test6(ptr %p, i64 %i1) {
 ; CHECK: ret i32 0
 }
 
+; P[i] != p[(i*4)|2048] with disjoint or
+define i32 @test6_higheror(ptr %p, i64 %i1) {
+  %i = shl nuw nsw i64 %i1, 2
+  %pi = getelementptr i32, ptr %p, i64 %i
+  %i.next = or disjoint i64 %i, 2048
+  %pi.next = getelementptr i32, ptr %p, i64 %i.next
+  %x = load i32, ptr %pi
+  store i32 42, ptr %pi.next
+  %y = load i32, ptr %pi
+  %z = sub i32 %x, %y
+  ret i32 %z
+; CHECK-LABEL: @test6_higheror(
+; CHECK: ret i32 0
+}
+
 ; P[1] != P[i*4]
 define i32 @test7(ptr %p, i64 %i) {
   %pi = getelementptr i32, ptr %p, i64 1