[llvm] r269387 - [LoopUnrollAnalyzer] Don't treat gep-instructions with simplified offset as simplified.

[Michael Zolotukhin via llvm-commits]

Author: mzolotukhin
Date: Thu May 12 20:42:34 2016
New Revision: 269387

URL: http://llvm.org/viewvc/llvm-project?rev=269387&view=rev
Log:
[LoopUnrollAnalyzer] Don't treat gep-instructions with simplified offset as simplified.

Summary:
Currently we consider such instructions as simplified, which is incorrect,
because if their user isn't simplified, we can't actually simplify them too.
This biases our estimates of profitability: for instance the analyzer expects
much more gains from unrolling memcpy loops than there actually are.

Reviewers: hfinkel, chandlerc

Subscribers: mzolotukhin, llvm-commits

Differential Revision: http://reviews.llvm.org/D17365

Added:
    llvm/trunk/test/Transforms/LoopUnroll/full-unroll-heuristics-geps.ll
Modified:
    llvm/trunk/lib/Analysis/LoopUnrollAnalyzer.cpp
    llvm/trunk/test/Transforms/LoopUnroll/full-unroll-heuristics-cmp.ll

Modified: llvm/trunk/lib/Analysis/LoopUnrollAnalyzer.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/LoopUnrollAnalyzer.cpp?rev=269387&r1=269386&r2=269387&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/LoopUnrollAnalyzer.cpp (original)
+++ llvm/trunk/lib/Analysis/LoopUnrollAnalyzer.cpp Thu May 12 20:42:34 2016
@@ -59,7 +59,7 @@ bool UnrolledInstAnalyzer::simplifyInstW
   Address.Base = Base->getValue();
   Address.Offset = Offset->getValue();
   SimplifiedAddresses[I] = Address;
-  return true;
+  return false;
 }
 
 /// Try to simplify binary operator I.

Modified: llvm/trunk/test/Transforms/LoopUnroll/full-unroll-heuristics-cmp.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/LoopUnroll/full-unroll-heuristics-cmp.ll?rev=269387&r1=269386&r2=269387&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/LoopUnroll/full-unroll-heuristics-cmp.ll (original)
+++ llvm/trunk/test/Transforms/LoopUnroll/full-unroll-heuristics-cmp.ll Thu May 12 20:42:34 2016
@@ -1,4 +1,4 @@
-; RUN: opt < %s -S -loop-unroll -unroll-max-iteration-count-to-analyze=100 -unroll-dynamic-cost-savings-discount=1000 -unroll-threshold=10 -unroll-percent-dynamic-cost-saved-threshold=50 | FileCheck %s
+; RUN: opt < %s -S -loop-unroll -unroll-max-iteration-count-to-analyze=100 -unroll-dynamic-cost-savings-discount=1000 -unroll-threshold=10 -unroll-percent-dynamic-cost-saved-threshold=40 | FileCheck %s
 target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
 
 @known_constant = internal unnamed_addr constant [10 x i32] [i32 1, i32 1, i32 1, i32 1, i32 1, i32 1, i32 1, i32 1, i32 1, i32 1], align 16

Added: llvm/trunk/test/Transforms/LoopUnroll/full-unroll-heuristics-geps.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/LoopUnroll/full-unroll-heuristics-geps.ll?rev=269387&view=auto
==============================================================================
--- llvm/trunk/test/Transforms/LoopUnroll/full-unroll-heuristics-geps.ll (added)
+++ llvm/trunk/test/Transforms/LoopUnroll/full-unroll-heuristics-geps.ll Thu May 12 20:42:34 2016
@@ -0,0 +1,28 @@
+; RUN: opt < %s -S -loop-unroll -unroll-max-iteration-count-to-analyze=100 -unroll-dynamic-cost-savings-discount=1000 -unroll-threshold=10 -unroll-percent-dynamic-cost-saved-threshold=40 | FileCheck %s
+target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
+
+; When examining gep-instructions we shouldn't consider them simplified if the
+; corresponding memory access isn't simplified. Doing the opposite might bias
+; our estimate, so that we might decide to unroll even a simple memcpy loop.
+;
+; Thus, the following loop shouldn't be unrolled:
+; CHECK-LABEL: @not_simplified_geps
+; CHECK: br i1 %
+; CHECK: ret void
+define void @not_simplified_geps(i32* noalias %b, i32* noalias %c) {
+entry:
+  br label %for.body
+
+for.body:
+  %iv.0 = phi i64 [ 0, %entry ], [ %iv.1, %for.body ]
+  %arrayidx1 = getelementptr inbounds i32, i32* %b, i64 %iv.0
+  %x1 = load i32, i32* %arrayidx1, align 4
+  %arrayidx2 = getelementptr inbounds i32, i32* %c, i64 %iv.0
+  store i32 %x1, i32* %arrayidx2, align 4
+  %iv.1 = add nuw nsw i64 %iv.0, 1
+  %exitcond = icmp eq i64 %iv.1, 10
+  br i1 %exitcond, label %for.end, label %for.body
+
+for.end:
+  ret void
+}