[PATCH] D25075: [LazyValueInfo] Understand monotonically increasing loops and identity values

[James Molloy via llvm-commits]

jmolloy updated this revision to Diff 74991.
jmolloy added a comment.

Hi Philip,

Thanks again. I've separated out the first, trivial, change and isolated a testcase for it.

I'm fairly sure the cache invalidation is required, but I will make that case in a followup phab review with the rest of the code as you suggested.

Cheers,
James


Repository:
  rL LLVM

https://reviews.llvm.org/D25075

Files:
  lib/Analysis/LazyValueInfo.cpp
  test/Transforms/CorrelatedValuePropagation/identity.ll


Index: test/Transforms/CorrelatedValuePropagation/identity.ll
===================================================================
--- /dev/null
+++ test/Transforms/CorrelatedValuePropagation/identity.ll
@@ -0,0 +1,30 @@
+; RUN: opt -S < %s -correlated-propagation | FileCheck %s
+
+; CHECK-LABEL: @f
+; CHECK: ret i32 3
+define i32 @f(i32 %n) {
+entry:
+  br label %while.cond
+
+while.cond:
+  %i = phi i32 [ 2, %entry ], [ %i, %one ], [ 3, %two ]
+  %cmp = icmp slt i32 %i, 3
+  br i1 %cmp, label %while.body, label %return
+
+while.body:
+  %call = call i32 @g(i32 1)
+  %add = add i32 %i, 6
+  %cmp3 = icmp sgt i32 %add , 6
+  br i1 %cmp3, label %one, label %two
+
+one:
+  br label %while.cond
+
+two:
+  br label %while.cond
+
+return:
+  ret i32 %i
+}
+
+declare i32 @g(i32)
Index: lib/Analysis/LazyValueInfo.cpp
===================================================================
--- lib/Analysis/LazyValueInfo.cpp
+++ lib/Analysis/LazyValueInfo.cpp
@@ -930,6 +930,11 @@
     if (EdgesMissing)
       continue;
 
+    // If this is an identity arc, we cannot be less specific now than we were
+    // before.
+    if (PhiVal == PN)
+      EdgeResult = intersect(EdgeResult, Result);
+
     Result.mergeIn(EdgeResult, DL);
 
     // If we hit overdefined, exit early.  The BlockVals entry is already set


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