[InferAlignment] Enhance alignment propagation for and(ptrtoint, const) pattern. (#166935)

Fixes: #152797

alive2: https://alive2.llvm.org/ce/z/h8HYTo
godbolt: https://godbolt.org/z/Mqzs9W8q4

Author: egorshamshura

llvm/lib/Transforms/Scalar/InferAlignment.cpp

@@ -12,15 +12,20 @@
 //===----------------------------------------------------------------------===//
 
 #include "llvm/Transforms/Scalar/InferAlignment.h"
+#include "llvm/ADT/APInt.h"
+#include "llvm/ADT/STLFunctionalExtras.h"
 #include "llvm/Analysis/AssumptionCache.h"
 #include "llvm/Analysis/ValueTracking.h"
+#include "llvm/IR/Instruction.h"
 #include "llvm/IR/Instructions.h"
 #include "llvm/IR/IntrinsicInst.h"
+#include "llvm/IR/PatternMatch.h"
 #include "llvm/Support/KnownBits.h"
 #include "llvm/Transforms/Scalar.h"
 #include "llvm/Transforms/Utils/Local.h"
 
 using namespace llvm;
+using namespace llvm::PatternMatch;
 
 static bool tryToImproveAlign(
     const DataLayout &DL, Instruction *I,
@@ -37,6 +42,16 @@ static bool tryToImproveAlign(
     }
   }
 
+  Value *PtrOp;
+  const APInt *Const;
+  if (match(I, m_And(m_PtrToIntOrAddr(m_Value(PtrOp)), m_APInt(Const)))) {
+    Align ActualAlign = Fn(PtrOp, Align(1), Align(1));
+    if (Const->ult(ActualAlign.value())) {
+      I->replaceAllUsesWith(Constant::getNullValue(I->getType()));
+      return true;
+    }
+  }
+
   IntrinsicInst *II = dyn_cast<IntrinsicInst>(I);
   if (!II)
     return false;

llvm/test/Transforms/InferAlignment/ptrtoint.ll

@@ -0,0 +1,64 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 6
+; RUN: opt < %s -passes=infer-alignment -S | FileCheck %s
+
+define i64 @base(ptr %ptr) {
+; CHECK-LABEL: define i64 @base(
+; CHECK-SAME: ptr [[PTR:%.*]]) {
+; CHECK-NEXT:    [[V1:%.*]] = load i32, ptr [[PTR]], align 4
+; CHECK-NEXT:    [[V3:%.*]] = ptrtoint ptr [[PTR]] to i64
+; CHECK-NEXT:    [[V5:%.*]] = and i64 [[V3]], 2
+; CHECK-NEXT:    ret i64 0
+;
+  %v1 = load i32, ptr %ptr, align 4
+  %v3 = ptrtoint ptr %ptr to i64
+  %v5 = and i64 %v3, 2
+  ret i64 %v5
+}
+
+define i64 @best_alignment(ptr %ptr) {
+; CHECK-LABEL: define i64 @best_alignment(
+; CHECK-SAME: ptr [[PTR:%.*]]) {
+; CHECK-NEXT:    [[V1:%.*]] = load i32, ptr [[PTR]], align 8
+; CHECK-NEXT:    [[V2:%.*]] = load i32, ptr [[PTR]], align 16
+; CHECK-NEXT:    [[V3:%.*]] = ptrtoint ptr [[PTR]] to i64
+; CHECK-NEXT:    [[V5:%.*]] = and i64 [[V3]], 15
+; CHECK-NEXT:    ret i64 0
+;
+  %v1 = load i32, ptr %ptr, align 8
+  %v2 = load i32, ptr %ptr, align 16
+  %v3 = ptrtoint ptr %ptr to i64
+  %v5 = and i64 %v3, 15
+  ret i64 %v5
+}
+
+declare void @func()
+
+define i64 @negative_test(ptr %ptr) {
+; CHECK-LABEL: define i64 @negative_test(
+; CHECK-SAME: ptr [[PTR:%.*]]) {
+; CHECK-NEXT:    [[V3:%.*]] = ptrtoint ptr [[PTR]] to i64
+; CHECK-NEXT:    [[V5:%.*]] = and i64 [[V3]], 2
+; CHECK-NEXT:    call void @func()
+; CHECK-NEXT:    [[V1:%.*]] = load i32, ptr [[PTR]], align 4
+; CHECK-NEXT:    ret i64 [[V5]]
+;
+  %v3 = ptrtoint ptr %ptr to i64
+  %v5 = and i64 %v3, 2
+  call void @func()
+  %v1 = load i32, ptr %ptr, align 4
+  ret i64 %v5
+}
+
+define i64 @ptrtoaddr(ptr %ptr) {
+; CHECK-LABEL: define i64 @ptrtoaddr(
+; CHECK-SAME: ptr [[PTR:%.*]]) {
+; CHECK-NEXT:    [[V3:%.*]] = ptrtoaddr ptr [[PTR]] to i64
+; CHECK-NEXT:    [[V1:%.*]] = load i32, ptr [[PTR]], align 4
+; CHECK-NEXT:    [[V5:%.*]] = and i64 [[V3]], 2
+; CHECK-NEXT:    ret i64 0
+;
+  %v3 = ptrtoaddr ptr %ptr to i64
+  %v1 = load i32, ptr %ptr, align 4
+  %v5 = and i64 %v3, 2
+  ret i64 %v5
+}