Support check alias between two instructions using getModRefInfo

Author: Chengjunp

llvm/include/llvm/Analysis/AliasAnalysis.h

@@ -381,6 +381,14 @@ class AAResults {
                      MemoryLocation::getBeforeOrAfter(V2));
   }
 
+  /// A convenience wrapper around the \c isNoAlias for two instructions.
+  bool isNoAlias(const Instruction *I1, const Instruction *I2) {
+    return getModRefInfo(&*I1, MemoryLocation::getOrNone(&*I2)) ==
+               ModRefInfo::NoModRef &&
+           getModRefInfo(&*I2, MemoryLocation::getOrNone(&*I1)) ==
+               ModRefInfo::NoModRef;
+  }
+
   /// A trivial helper function to check to see if the specified pointers are
   /// must-alias.
   bool isMustAlias(const MemoryLocation &LocA, const MemoryLocation &LocB) {

llvm/lib/Transforms/Utils/FlattenCFG.cpp

@@ -357,12 +357,8 @@ bool FlattenCFGOpt::CompareIfRegionBlock(BasicBlock *Block1, BasicBlock *Block2,
       for (BasicBlock::iterator BI(PBI2), BE(PTI2); BI != BE; ++BI) {
         if (BI->mayReadFromMemory() || BI->mayWriteToMemory()) {
           // Check alias with Head2.
-          if (AA) {
-            MemoryLocation Loc1 = MemoryLocation::get(&*iter1);
-            MemoryLocation Loc2 = MemoryLocation::get(&*BI);
-            if (!AA->isNoAlias(Loc1, Loc2))
-              return false;
-          }
+          if (!AA || !AA->isNoAlias(&*iter1, &*BI))
+            return false;
         }
       }
     }

llvm/test/Transforms/Util/flatten-cfg.ll

@@ -1,5 +1,5 @@
 ; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 2
-; RUN: opt -passes='require<aa>,flatten-cfg' -S < %s | FileCheck %s
+; RUN: opt -passes=flatten-cfg -S < %s | FileCheck %s
 
 
 ; This test checks whether the pass completes without a crash.
@@ -310,6 +310,9 @@ exit:
   ret i1 %cmp.y
 }
 
+declare void @foo()
+declare void @bar() #1
+
 ; Test that two if-regions are not merged when there's potential aliasing
 ; between a store in the first if-region and a load in the second if-region's header
 define i32 @test_alias(i32 %a, i32 %b, ptr %p1, ptr %p2) {
@@ -354,6 +357,52 @@ if.end2:
   ret i32 0
 }
 
+; Test that two if-regions are not merged when there's potential aliasing
+; between a fuction call in the first if-region and a load in the second if-region's header
+define i32 @test_alias_2(i32 %a, i32 %b) {
+; CHECK-LABEL: define i32 @test_alias_2
+; CHECK-SAME: (i32 [[A:%.*]], i32 [[B:%.*]]) {
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[P:%.*]] = alloca i32, align 4
+; CHECK-NEXT:    store i32 42, ptr [[P]], align 4
+; CHECK-NEXT:    [[COND1:%.*]] = icmp eq i32 [[A]], 0
+; CHECK-NEXT:    br i1 [[COND1]], label [[IF_THEN1:%.*]], label [[IF_END1:%.*]]
+; CHECK:       if.then1:
+; CHECK-NEXT:    call void @foo()
+; CHECK-NEXT:    br label [[IF_END1]]
+; CHECK:       if.end1:
+; CHECK-NEXT:    [[VAL:%.*]] = load i32, ptr @g, align 4
+; CHECK-NEXT:    [[COND2:%.*]] = icmp eq i32 [[B]], 0
+; CHECK-NEXT:    br i1 [[COND2]], label [[IF_THEN2:%.*]], label [[IF_END2:%.*]]
+; CHECK:       if.then2:
+; CHECK-NEXT:    call void @foo()
+; CHECK-NEXT:    br label [[IF_END2]]
+; CHECK:       if.end2:
+; CHECK-NEXT:    ret i32 0
+;
+entry:
+  %p = alloca i32
+  store i32 42, ptr %p
+  %cond1 = icmp eq i32 %a, 0
+  br i1 %cond1, label %if.then1, label %if.end1
+
+if.then1:
+  call void @foo()
+  br label %if.end1
+
+if.end1:
+  %val = load i32, ptr @g
+  %cond2 = icmp eq i32 %b, 0
+  br i1 %cond2, label %if.then2, label %if.end2
+
+if.then2:
+  call void @foo()
+  br label %if.end2
+
+if.end2:
+  ret i32 0
+}
+
 ; Test that two if-regions are merged when there's no potential aliasing
 ; between a store in the first if-region and a load in the second if-region's header
 define i32 @test_no_alias(i32 %a, i32 %b) {
@@ -369,18 +418,20 @@ define i32 @test_no_alias(i32 %a, i32 %b) {
 ; CHECK-NEXT:    br i1 [[TMP0]], label [[IF_THEN2:%.*]], label [[IF_END2:%.*]]
 ; CHECK:       if.then2:
 ; CHECK-NEXT:    store i32 100, ptr [[P]], align 4
+; CHECK-NEXT:    call void @bar()
 ; CHECK-NEXT:    br label [[IF_END2]]
 ; CHECK:       if.end2:
 ; CHECK-NEXT:    ret i32 0
 ;
-  entry:
+entry:
   %p = alloca i32
   store i32 42, ptr %p
   %cond1 = icmp eq i32 %a, 0
   br i1 %cond1, label %if.then1, label %if.end1
 
 if.then1:
   store i32 100, ptr %p  ; No alias with the load below
+  call void @bar() ; No alias with the load below since it's a pure function
   br label %if.end1
 
 if.end1:
@@ -390,8 +441,11 @@ if.end1:
 
 if.then2:
   store i32 100, ptr %p
+  call void @bar()
   br label %if.end2
 
 if.end2:
   ret i32 0
-}
+}
+
+attributes #1 = { readnone willreturn nounwind }