From: David Majnemer <david.majnemer@gmail.com>
Date: Thu, 7 Jan 2016 19:25:39 +0000 (+0000)
Subject: [SCCP] Can't go from overdefined to constant
X-Git-Url: http://plrg.eecs.uci.edu/git/?p=oota-llvm.git;a=commitdiff_plain;h=e9b0c81b34562003bbe86393d6cc291249dcece0

[SCCP] Can't go from overdefined to constant

The fix for PR23999 made us mark loads of null as producing the constant
undef which upsets the lattice.  Instead, keep the load as "undefined".
This fixes PR26044.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@257087 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/Transforms/Scalar/SCCP.cpp b/lib/Transforms/Scalar/SCCP.cpp
index 2fca803adde..c5e2e9f3f79 100644
--- a/lib/Transforms/Scalar/SCCP.cpp
+++ b/lib/Transforms/Scalar/SCCP.cpp
@@ -1047,7 +1047,7 @@ void SCCPSolver::visitStoreInst(StoreInst &SI) {
 // global, we can replace the load with the loaded constant value!
 void SCCPSolver::visitLoadInst(LoadInst &I) {
   // If this load is of a struct, just mark the result overdefined.
-  if (I.getType()->isStructTy())
+  if (I.getType()->isStructTy() || I.getType()->isMMXTy())
     return markAnythingOverdefined(&I);
 
   LatticeVal PtrVal = getValueState(I.getOperand(0));
@@ -1061,9 +1061,9 @@ void SCCPSolver::visitLoadInst(LoadInst &I) {
 
   Constant *Ptr = PtrVal.getConstant();
 
-  // load null -> null
+  // load null is undefined.
   if (isa<ConstantPointerNull>(Ptr) && I.getPointerAddressSpace() == 0)
-    return markConstant(IV, &I, UndefValue::get(I.getType()));
+    return;
 
   // Transform load (constant global) into the value loaded.
   if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Ptr)) {
diff --git a/test/Transforms/IPConstantProp/PR26044.ll b/test/Transforms/IPConstantProp/PR26044.ll
new file mode 100644
index 00000000000..9e8c61eb53b
--- /dev/null
+++ b/test/Transforms/IPConstantProp/PR26044.ll
@@ -0,0 +1,31 @@
+; RUN: opt < %s -S -ipsccp | FileCheck %s
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+define void @fn2() {
+entry:
+  br label %if.end
+
+for.cond1:                                        ; preds = %if.end, %for.end
+  br i1 undef, label %if.end, label %if.end
+
+if.end:                                           ; preds = %lbl, %for.cond1
+  %e.2 = phi i32* [ undef, %entry ], [ null, %for.cond1 ], [ null, %for.cond1 ]
+  %0 = load i32, i32* %e.2, align 4
+  %call = call i32 @fn1(i32 %0)
+  br label %for.cond1
+}
+
+define internal i32 @fn1(i32 %p1) {
+entry:
+  %tobool = icmp ne i32 %p1, 0
+  %cond = select i1 %tobool, i32 %p1, i32 %p1
+  ret i32 %cond
+}
+
+; CHECK-LABEL: define void @fn2(
+; CHECK: call i32 @fn1(i32 undef)
+
+; CHECK-LABEL: define internal i32 @fn1(
+; CHECK:%[[COND:.*]] = select i1 undef, i32 undef, i32 undef
+; CHECK: ret i32 %[[COND]]