[instsimplify] Assume storage for byval args doesn't overlap allocas,…

… globals, or other byval args This allows us to discharge many pointer comparisons based on byval arguments. Differential Revision: https://reviews.llvm.org/D120133
llvm · Feb 18, 2022 · ff2e4c0 · ff2e4c0
1 parent eae62b2
commit ff2e4c0
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Showing 2 changed files with 25 additions and 13 deletions.
diff --git a/llvm/lib/Analysis/InstructionSimplify.cpp b/llvm/lib/Analysis/InstructionSimplify.cpp
@@ -2555,7 +2555,19 @@ static bool HaveNonOverlappingStorage(const Value *V1, const Value *V2) {
   //
   // So, we'll assume that two non-empty allocas have different addresses
   // for now.
-  return isa<AllocaInst>(V1) &&
+  auto isByValArg = [](const Value *V) {
+    const Argument *A = dyn_cast<Argument>(V);
+    return A && A->hasByValAttr();
+  };
+
+  // Byval args are backed by store which does not overlap with each other,
+  // allocas, or globals.
+  if (isByValArg(V1))
+    return isa<AllocaInst>(V2) || isa<GlobalVariable>(V2) || isByValArg(V2);
+  if (isByValArg(V2))
+    return isa<AllocaInst>(V1) || isa<GlobalVariable>(V1) || isByValArg(V1);
+
+ return isa<AllocaInst>(V1) &&
     (isa<AllocaInst>(V2) || isa<GlobalVariable>(V2));
 }
 
@@ -2659,8 +2671,12 @@ computePointerICmp(CmpInst::Predicate Pred, Value *LHS, Value *RHS,
       uint64_t LHSSize, RHSSize;
       ObjectSizeOpts Opts;
       Opts.EvalMode = ObjectSizeOpts::Mode::Min;
-      Opts.NullIsUnknownSize =
-          NullPointerIsDefined(cast<AllocaInst>(LHS)->getFunction());
+      auto *F = [](Value *V) {
+        if (auto *I = dyn_cast<Instruction>(V))
+          return I->getFunction();
+        return cast<Argument>(V)->getParent();
+      }(LHS);
+      Opts.NullIsUnknownSize = NullPointerIsDefined(F);
       if (getObjectSize(LHS, LHSSize, DL, TLI, Opts) &&
           getObjectSize(RHS, RHSSize, DL, TLI, Opts) &&
           !LHSOffset.isNegative() && !RHSOffset.isNegative() &&

diff --git a/llvm/test/Transforms/InstSimplify/compare.ll b/llvm/test/Transforms/InstSimplify/compare.ll
@@ -2737,11 +2737,10 @@ define i1 @scalar_vectors_are_non_empty() {
   ret i1 %res
 }
 
-; TODO: Never equal
+; Never equal
 define i1 @byval_args_inequal(i32* byval(i32) %a, i32* byval(i32) %b) {
 ; CHECK-LABEL: @byval_args_inequal(
-; CHECK-NEXT:    [[RES:%.*]] = icmp ne i32* [[A:%.*]], [[B:%.*]]
-; CHECK-NEXT:    ret i1 [[RES]]
+; CHECK-NEXT:    ret i1 true
 ;
   %res = icmp ne i32* %a, %b
   ret i1 %res
@@ -2759,12 +2758,10 @@ define i1 @neg_args_adjacent(i32* byval(i32) %a, i32* byval(i32) %b) {
   ret i1 %res
 }
 
-; TODO: Never equal
+; Never equal
 define i1 @test_byval_alloca_inequal(i32* byval(i32) %a) {
 ; CHECK-LABEL: @test_byval_alloca_inequal(
-; CHECK-NEXT:    [[B:%.*]] = alloca i32, align 4
-; CHECK-NEXT:    [[RES:%.*]] = icmp ne i32* [[A:%.*]], [[B]]
-; CHECK-NEXT:    ret i1 [[RES]]
+; CHECK-NEXT:    ret i1 true
 ;
   %b = alloca i32
   %res = icmp ne i32* %a, %b
@@ -2812,11 +2809,10 @@ define i1 @globals_offset_inequal() {
 }
 
 
-; TODO: Never equal
+; Never equal
 define i1 @test_byval_global_inequal(i32* byval(i32) %a) {
 ; CHECK-LABEL: @test_byval_global_inequal(
-; CHECK-NEXT:    [[RES:%.*]] = icmp ne i32* [[A:%.*]], @B
-; CHECK-NEXT:    ret i1 [[RES]]
+; CHECK-NEXT:    ret i1 true
 ;
   %b = alloca i32
   %res = icmp ne i32* %a, @B