Fix bug in rewriting of library calls to intrinsics + new regression test.

The pass gets confused in some cases when library functions get passed to
other functions as arguments, because use_iterator returns the call instruction.
The existing test (rewrite-longjmp-noncall-uses.ll) did not catch this problem
because there a bitcast constexpr was applied to the library function pointer,
and it came up as the use instead of the containing call.

BUG=https://code.google.com/p/nativeclient/issues/detail?id=3706
R=mseaborn@chromium.org

Review URL: https://codereview.chromium.org/26952003

1 files changed, 7 insertions, 2 deletions

diff --git a/lib/Transforms/NaCl/RewritePNaClLibraryCalls.cpp b/lib/Transforms/NaCl/RewritePNaClLibraryCalls.cpp
index a01e8c6b2a..6656a672fe 100644
--- a/lib/Transforms/NaCl/RewritePNaClLibraryCalls.cpp
+++ b/lib/Transforms/NaCl/RewritePNaClLibraryCalls.cpp
@@ -171,9 +171,14 @@ bool RewritePNaClLibraryCalls::RewriteLibraryCall(
     for (Value::use_iterator UI = LibFunc->use_begin(),
                              UE = LibFunc->use_end(); UI != UE;) {
       Value *Use = *UI++;
+      // use_iterator will also provide call instructions in which the used
+      // value is an argument, and not the value being called. Make sure we
+      // rewrite only actual calls to LibFunc here.
       if (CallInst *Call = dyn_cast<CallInst>(Use)) {
-        (this->*(CallRewriter))(Call);
-        Changed = true;
+        if (Call->getCalledValue() == LibFunc) {
+          (this->*(CallRewriter))(Call);
+          Changed = true;
+        }
       }
     }