From 8967e18c4a7c2bc9dd88c40a68368da68b452062 Mon Sep 17 00:00:00 2001
From: John Brawn <john.brawn@arm.com>
Date: Mon, 10 Sep 2018 12:23:05 +0000
Subject: [PATCH] [GVN] Invalidate cached info for values replaced by equality
 propagation

When GVN propagates an equality by replacing one value with another it also
needs to invalidate the cached information for the value being replaced.

Differential Revision: https://reviews.llvm.org/D51218

llvm-svn: 341820
---
 llvm/lib/Transforms/Scalar/GVN.cpp   |  6 +++
 llvm/test/Transforms/GVN/condprop.ll | 72 ++++++++++++++++++++++++++++++++++++
 2 files changed, 78 insertions(+)

diff --git a/llvm/lib/Transforms/Scalar/GVN.cpp b/llvm/lib/Transforms/Scalar/GVN.cpp
index c48e766..95c35ad 100644
--- a/llvm/lib/Transforms/Scalar/GVN.cpp
+++ b/llvm/lib/Transforms/Scalar/GVN.cpp
@@ -1736,6 +1736,9 @@ bool GVN::propagateEquality(Value *LHS, Value *RHS, const BasicBlockEdge &Root,
 
       Changed |= NumReplacements > 0;
       NumGVNEqProp += NumReplacements;
+      // Cached information for anything that uses LHS will be invalid.
+      if (MD)
+        MD->invalidateCachedPointerInfo(LHS);
     }
 
     // Now try to deduce additional equalities from this one. For example, if
@@ -1811,6 +1814,9 @@ bool GVN::propagateEquality(Value *LHS, Value *RHS, const BasicBlockEdge &Root,
                                              Root.getStart());
           Changed |= NumReplacements > 0;
           NumGVNEqProp += NumReplacements;
+          // Cached information for anything that uses NotCmp will be invalid.
+          if (MD)
+            MD->invalidateCachedPointerInfo(NotCmp);
         }
       }
       // Ensure that any instruction in scope that gets the "A < B" value number
diff --git a/llvm/test/Transforms/GVN/condprop.ll b/llvm/test/Transforms/GVN/condprop.ll
index 6aa3cb8..949fdd0 100644
--- a/llvm/test/Transforms/GVN/condprop.ll
+++ b/llvm/test/Transforms/GVN/condprop.ll
@@ -297,3 +297,75 @@ ret:
 ; CHECK: %res = phi i32 [ 0, %cond_true ], [ %x, %cond_false ]
   ret i32 %res
 }
+
+; On the path from entry->if->end we know that ptr1==ptr2, so we can determine
+; that gep2 does not alias ptr1 on that path (as it would require that
+; ptr2==ptr2+2), so we can perform PRE of the load.
+; CHECK-LABEL: @test13
+define i32 @test13(i32* %ptr1, i32* %ptr2) {
+; CHECK-LABEL: entry:
+entry:
+  %gep1 = getelementptr i32, i32* %ptr2, i32 1
+  %gep2 = getelementptr i32, i32* %ptr2, i32 2
+  %cmp = icmp eq i32* %ptr1, %ptr2
+  br i1 %cmp, label %if, label %end
+
+; CHECK: [[CRIT_EDGE:.*]]:
+; CHECK: %[[PRE:.*]] = load i32, i32* %gep2, align 4
+
+; CHECK-LABEL: if:
+if:
+  %val1 = load i32, i32* %gep2, align 4
+  br label %end
+
+; CHECK-LABEL: end:
+; CHECK: %val2 = phi i32 [ %val1, %if ], [ %[[PRE]], %[[CRIT_EDGE]] ]
+; CHECK-NOT: load
+end:
+  %phi1 = phi i32* [ %ptr1, %if ], [ %gep1, %entry ]
+  %phi2 = phi i32 [ %val1, %if ], [ 0, %entry ]
+  store i32 0, i32* %phi1, align 4
+  %val2 = load i32, i32* %gep2, align 4
+  %ret = add i32 %phi2, %val2
+  ret i32 %ret
+}
+
+; CHECK-LABEL: @test14
+define void @test14(i32* %ptr1, i32* noalias %ptr2) {
+entry:
+  %gep1 = getelementptr inbounds i32, i32* %ptr1, i32 1
+  %gep2 = getelementptr inbounds i32, i32* %ptr1, i32 2
+  br label %loop
+
+; CHECK-LABEL: loop:
+loop:
+  %phi1 = phi i32* [ %gep3, %loop.end ], [ %gep1, %entry ]
+  br i1 undef, label %if1, label %then
+
+; CHECK: [[CRIT_EDGE:.*]]:
+; CHECK: %[[PRE:.*]] = load i32, i32* %gep2, align 4
+
+; CHECK-LABEL: if1:
+; CHECK: %val2 = phi i32 [ %[[PRE]], %[[CRIT_EDGE]] ], [ %val3, %loop.end ]
+; CHECK-NOT: load
+if1:
+  %val2 = load i32, i32* %gep2, align 4
+  store i32 %val2, i32* %gep2, align 4
+  store i32 0, i32* %phi1, align 4
+  br label %then
+
+; CHECK-LABEL: then:
+then:
+  %cmp = icmp eq i32* %gep2, %ptr2
+  br i1 %cmp, label %loop.end, label %if2
+
+if2:
+  br label %loop.end
+
+loop.end:
+  %phi3 = phi i32* [ %gep2, %then ], [ %ptr1, %if2 ]
+  %val3 = load i32, i32* %gep2, align 4
+  store i32 %val3, i32* %phi3, align 4
+  %gep3 = getelementptr inbounds i32, i32* %ptr1, i32 1
+  br i1 undef, label %loop, label %if1
+}
-- 
2.7.4