Do not widen load for different variable in GVN.

Summary:
Widening load in GVN is too early because it will block other optimizations like PRE, LICM.

https://llvm.org/bugs/show_bug.cgi?id=29110

The SPECCPU2006 benchmark impact of this patch:

Reference: o2_nopatch
(1): o2_patched

           Benchmark             Base:Reference   (1)  
-------------------------------------------------------
spec/2006/fp/C++/444.namd                  25.2  -0.08%
spec/2006/fp/C++/447.dealII               45.92  +1.05%
spec/2006/fp/C++/450.soplex                41.7  -0.26%
spec/2006/fp/C++/453.povray               35.65  +1.68%
spec/2006/fp/C/433.milc                   23.79  +0.42%
spec/2006/fp/C/470.lbm                    41.88  -1.12%
spec/2006/fp/C/482.sphinx3                47.94  +1.67%
spec/2006/int/C++/471.omnetpp             22.46  -0.36%
spec/2006/int/C++/473.astar               21.19  +0.24%
spec/2006/int/C++/483.xalancbmk           36.09  -0.11%
spec/2006/int/C/400.perlbench             33.28  +1.35%
spec/2006/int/C/401.bzip2                 22.76  -0.04%
spec/2006/int/C/403.gcc                   32.36  +0.12%
spec/2006/int/C/429.mcf                   41.04  -0.41%
spec/2006/int/C/445.gobmk                 26.94  +0.04%
spec/2006/int/C/456.hmmer                  24.5  -0.20%
spec/2006/int/C/458.sjeng                    28  -0.46%
spec/2006/int/C/462.libquantum            55.25  +0.27%
spec/2006/int/C/464.h264ref               45.87  +0.72%

geometric mean                                   +0.23%

For most benchmarks, it's a wash, but we do see stable improvements on some benchmarks, e.g. 447,453,482,400.

Reviewers: davidxl, hfinkel, dberlin, sanjoy, reames

Subscribers: gberry, junbuml

Differential Revision: https://reviews.llvm.org/D24096

llvm-svn: 281074

7 files changed, 23 insertions, 54 deletions

diff --git a/llvm/lib/Analysis/MemoryDependenceAnalysis.cpp b/llvm/lib/Analysis/MemoryDependenceAnalysis.cpp
index fe0f6a2d261..bd3f7906084 100644
--- a/llvm/lib/Analysis/MemoryDependenceAnalysis.cpp
+++ b/llvm/lib/Analysis/MemoryDependenceAnalysis.cpp
@@ -234,26 +234,6 @@ MemDepResult MemoryDependenceResults::getCallSiteDependencyFrom(
   return MemDepResult::getNonFuncLocal();
 }
 
-/// Return true if LI is a load that would fully overlap MemLoc if done as
-/// a wider legal integer load.
-///
-/// MemLocBase, MemLocOffset are lazily computed here the first time the
-/// base/offs of memloc is needed.
-static bool isLoadLoadClobberIfExtendedToFullWidth(const MemoryLocation &MemLoc,
-                                                   const Value *&MemLocBase,
-                                                   int64_t &MemLocOffs,
-                                                   const LoadInst *LI) {
-  const DataLayout &DL = LI->getModule()->getDataLayout();
-
-  // If we haven't already computed the base/offset of MemLoc, do so now.
-  if (!MemLocBase)
-    MemLocBase = GetPointerBaseWithConstantOffset(MemLoc.Ptr, MemLocOffs, DL);
-
-  unsigned Size = MemoryDependenceResults::getLoadLoadClobberFullWidthSize(
-      MemLocBase, MemLocOffs, MemLoc.Size, LI);
-  return Size != 0;
-}
-
 unsigned MemoryDependenceResults::getLoadLoadClobberFullWidthSize(
     const Value *MemLocBase, int64_t MemLocOffs, unsigned MemLocSize,
     const LoadInst *LI) {
@@ -410,9 +390,6 @@ MemoryDependenceResults::getInvariantGroupPointerDependency(LoadInst *LI,
 MemDepResult MemoryDependenceResults::getSimplePointerDependencyFrom(
     const MemoryLocation &MemLoc, bool isLoad, BasicBlock::iterator ScanIt,
     BasicBlock *BB, Instruction *QueryInst, unsigned *Limit) {
-
-  const Value *MemLocBase = nullptr;
-  int64_t MemLocOffset = 0;
   bool isInvariantLoad = false;
 
   if (!Limit) {
@@ -550,21 +527,8 @@ MemDepResult MemoryDependenceResults::getSimplePointerDependencyFrom(
       AliasResult R = AA.alias(LoadLoc, MemLoc);
 
       if (isLoad) {
-        if (R == NoAlias) {
-          // If this is an over-aligned integer load (for example,
-          // "load i8* %P, align 4") see if it would obviously overlap with the
-          // queried location if widened to a larger load (e.g. if the queried
-          // location is 1 byte at P+1).  If so, return it as a load/load
-          // clobber result, allowing the client to decide to widen the load if
-          // it wants to.
-          if (IntegerType *ITy = dyn_cast<IntegerType>(LI->getType())) {
-            if (LI->getAlignment() * 8 > ITy->getPrimitiveSizeInBits() &&
-                isLoadLoadClobberIfExtendedToFullWidth(MemLoc, MemLocBase,
-                                                       MemLocOffset, LI))
-              return MemDepResult::getClobber(Inst);
-          }
+        if (R == NoAlias)
           continue;
-        }
 
         // Must aliased loads are defs of each other.
         if (R == MustAlias)
diff --git a/llvm/test/Instrumentation/AddressSanitizer/asan-vs-gvn.ll b/llvm/test/Instrumentation/AddressSanitizer/asan-vs-gvn.ll
index b5ef8f20689..052d56d21c0 100644
--- a/llvm/test/Instrumentation/AddressSanitizer/asan-vs-gvn.ll
+++ b/llvm/test/Instrumentation/AddressSanitizer/asan-vs-gvn.ll
@@ -34,7 +34,7 @@ define void @end_test_widening_bad() {
   ret void
 }
 
-;; Accessing bytes 4 and 5. Ok to widen to i16.
+;; Accessing bytes 4 and 5. No widen to i16.
 
 define i32 @test_widening_ok(i8* %P) nounwind ssp noredzone sanitize_address {
 entry:
@@ -45,7 +45,8 @@ entry:
   %add = add nsw i32 %conv, %conv2
   ret i32 %add
 ; CHECK: @test_widening_ok
-; CHECK: __asan_report_load2
+; CHECK: __asan_report_load1
+; CHECK: __asan_report_load1
 ; CHECK-NOT: __asan_report
 ; CHECK: end_test_widening_ok
 }
diff --git a/llvm/test/Transforms/GVN/PRE/load-pre-nonlocal.ll b/llvm/test/Transforms/GVN/PRE/load-pre-nonlocal.ll
index 1e5e0912cd7..65826fb9213 100644
--- a/llvm/test/Transforms/GVN/PRE/load-pre-nonlocal.ll
+++ b/llvm/test/Transforms/GVN/PRE/load-pre-nonlocal.ll
@@ -51,15 +51,16 @@ for.end:
 }
 
 ; %1 is partially redundant if %0 can be widened to a 64-bit load.
+; But we should not widen %0 to 64-bit load.
 
 ; CHECK-LABEL: define i32 @overaligned_load
 ; CHECK: if.then:
-; CHECK:   %0 = load i64
-; CHECK:   [[LSHR:%[0-9]+]] = lshr i64 %0, 32, !dbg [[LSHR_LOC:![0-9]+]]
-; CHECK:   trunc i64 [[LSHR]] to i32
+; CHECK-NOT:   %0 = load i64
+; CHECK-NOT:   [[LSHR:%[0-9]+]] = lshr i64 %0, 32, !dbg [[LSHR_LOC:![0-9]+]]
+; CHECK-NOT:   trunc i64 [[LSHR]] to i32
 ; CHECK: if.end:
-; CHECK-NOT: %1 = load i32, i32*
-; CHECK: [[LSHR_LOC]] = !DILocation(line: 101, column: 1, scope: !{{.*}})
+; CHECK: %1 = load i32, i32*
+; CHECK-NOT: [[LSHR_LOC]] = !DILocation(line: 101, column: 1, scope: !{{.*}})
 
 define i32 @overaligned_load(i32 %a, i32* nocapture %b) !dbg !13 {
 entry:
diff --git a/llvm/test/Transforms/GVN/PRE/rle.ll b/llvm/test/Transforms/GVN/PRE/rle.ll
index 3f42135b409..121fe6ebb3d 100644
--- a/llvm/test/Transforms/GVN/PRE/rle.ll
+++ b/llvm/test/Transforms/GVN/PRE/rle.ll
@@ -624,6 +624,7 @@ if.end:
 
 ;;===----------------------------------------------------------------------===;;
 ;; Load Widening
+;; We explicitly choose NOT to widen. And are testing to make sure we don't.
 ;;===----------------------------------------------------------------------===;;
 
 %widening1 = type { i32, i8, i8, i8, i8 }
@@ -640,7 +641,8 @@ entry:
   ret i32 %add
 ; CHECK-LABEL: @test_widening1(
 ; CHECK-NOT: load
-; CHECK: load i16, i16*
+; CHECK: load i8, i8*
+; CHECK: load i8, i8*
 ; CHECK-NOT: load
 ; CHECK: ret i32
 }
@@ -664,7 +666,10 @@ entry:
   ret i32 %add3
 ; CHECK-LABEL: @test_widening2(
 ; CHECK-NOT: load
-; CHECK: load i32, i32*
+; CHECK: load i8, i8*
+; CHECK: load i8, i8*
+; CHECK: load i8, i8*
+; CHECK: load i8, i8*
 ; CHECK-NOT: load
 ; CHECK: ret i32
 }
diff --git a/llvm/test/Transforms/GVN/big-endian.ll b/llvm/test/Transforms/GVN/big-endian.ll
index faaf3ef465b..f6b7374c17c 100644
--- a/llvm/test/Transforms/GVN/big-endian.ll
+++ b/llvm/test/Transforms/GVN/big-endian.ll
@@ -7,9 +7,9 @@ target triple = "powerpc64-unknown-linux-gnu"
 ;; loads reusing a load value.
 define i64 @test1({ i1, i8 }* %predA, { i1, i8 }* %predB) {
 ; CHECK-LABEL: @test1
-; CHECK: [[V1:%.*]] = load i16, i16* %{{.*}}
-; CHECK: [[V2:%.*]] = lshr i16 [[V1]], 8
-; CHECK: trunc i16 [[V2]] to i1
+; CHECK-NOT: [[V1:%.*]] = load i16, i16* %{{.*}}
+; CHECK-NOT: [[V2:%.*]] = lshr i16 [[V1]], 8
+; CHECK-NOT: trunc i16 [[V2]] to i1
 
   %valueLoadA.fca.0.gep = getelementptr inbounds { i1, i8 }, { i1, i8 }* %predA, i64 0, i32 0
   %valueLoadA.fca.0.load = load i1, i1* %valueLoadA.fca.0.gep, align 8
diff --git a/llvm/test/Transforms/GVN/no_speculative_loads_with_asan.ll b/llvm/test/Transforms/GVN/no_speculative_loads_with_asan.ll
index 2e790db1b2a..a83d7b62d39 100644
--- a/llvm/test/Transforms/GVN/no_speculative_loads_with_asan.ll
+++ b/llvm/test/Transforms/GVN/no_speculative_loads_with_asan.ll
@@ -25,9 +25,7 @@ define i32 @TestNoAsan() {
 }
 
 ; CHECK-LABEL: @TestNoAsan
-; CHECK: %[[LOAD:[^ ]+]] = load i32
-; CHECK: {{.*}} = ashr i32 %[[LOAD]]
-; CHECK-NOT: {{.*}} = phi
+; CHECK: ret i32 0
 
 define i32 @TestAsan() sanitize_address {
   %1 = tail call noalias i8* @_Znam(i64 2)
diff --git a/llvm/test/Transforms/GVN/pr25440.ll b/llvm/test/Transforms/GVN/pr25440.ll
index 14e2c30f04b..21ccc4e77b6 100644
--- a/llvm/test/Transforms/GVN/pr25440.ll
+++ b/llvm/test/Transforms/GVN/pr25440.ll
@@ -19,7 +19,7 @@ bb0:                                      ; preds = %land.lhs.true, %entry
   %x.tr = phi %struct.a* [ %x, %entry ], [ null, %land.lhs.true ]
   %code1 = getelementptr inbounds %struct.a, %struct.a* %x.tr, i32 0, i32 0
   %0 = load i16, i16* %code1, align 4
-; CHECK: load i32, i32*
+; CHECK: load i16, i16*
   %conv = zext i16 %0 to i32
   switch i32 %conv, label %if.end.50 [
     i32 43, label %cleanup
@@ -38,7 +38,7 @@ if.then.26:                                       ; preds = %if.then.5
 
 cond.false:                                       ; preds = %if.then.26
 ; CHECK: cond.false:
-; CHECK-NOT: load
+; CHECK: load i16
   %mode = getelementptr inbounds %struct.a, %struct.a* %x.tr.lcssa163, i32 0, i32 1
   %bf.load = load i16, i16* %mode, align 2
   %bf.shl = shl i16 %bf.load, 8