diff options
| -rw-r--r-- | lib/Transforms/Scalar/GVN.cpp | 8 | ||||
| -rw-r--r-- | test/Transforms/GVN/pre-single-pred.ll | 14 |
2 files changed, 20 insertions, 2 deletions
diff --git a/lib/Transforms/Scalar/GVN.cpp b/lib/Transforms/Scalar/GVN.cpp index 41ff18702d..de99c3f8b6 100644 --- a/lib/Transforms/Scalar/GVN.cpp +++ b/lib/Transforms/Scalar/GVN.cpp @@ -1532,8 +1532,14 @@ bool GVN::processNonLocalLoad(LoadInst *LI, return false; if (Blockers.count(TmpBB)) return false; + + // If any of these blocks has more than one successor (i.e. if the edge we + // just traversed was critical), then there are other paths through this + // block along which the load may not be anticipated. Hoisting the load + // above this block would be adding the load to execution paths along + // which it was not previously executed. if (TmpBB->getTerminator()->getNumSuccessors() != 1) - allSingleSucc = false; + return false; } assert(TmpBB); diff --git a/test/Transforms/GVN/pre-single-pred.ll b/test/Transforms/GVN/pre-single-pred.ll index 706a16b7bd..f1f5c71a93 100644 --- a/test/Transforms/GVN/pre-single-pred.ll +++ b/test/Transforms/GVN/pre-single-pred.ll @@ -1,4 +1,13 @@ -; RUN: opt < %s -gvn -enable-load-pre -S | not grep {tmp3 = load} +; RUN: opt < %s -gvn -enable-load-pre -S | FileCheck %s +; This testcase assumed we'll PRE the load into %for.cond, but we don't actually +; verify that doing so is safe. If there didn't _happen_ to be a load in +; %for.end, we would actually be lengthening the execution on some paths, and +; we were never actually checking that case. Now we actually do perform some +; conservative checking to make sure we don't make paths longer, but we don't +; currently get this case, which we got lucky on previously. +; +; Now that that faulty assumption is corrected, test that we DON'T incorrectly +; hoist the load. Doing the right thing for the wrong reasons is still a bug. @p = external global i32 define i32 @f(i32 %n) nounwind { @@ -13,6 +22,8 @@ for.cond: ; preds = %for.inc, %entry for.cond.for.end_crit_edge: ; preds = %for.cond br label %for.end +; CHECK: for.body: +; CHECK-NEXT: %tmp3 = load i32* @p for.body: ; preds = %for.cond %tmp3 = load i32* @p ; <i32> [#uses=1] %dec = add i32 %tmp3, -1 ; <i32> [#uses=2] @@ -20,6 +31,7 @@ for.body: ; preds = %for.cond %cmp6 = icmp slt i32 %dec, 0 ; <i1> [#uses=1] br i1 %cmp6, label %for.body.for.end_crit_edge, label %for.inc +; CHECK: for.body.for.end_crit_edge: for.body.for.end_crit_edge: ; preds = %for.body br label %for.end |