[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 2fca803adde80b0a0b095ddda4d30a9551f86b86..c5e2e9f3f79921981b3dd3b37fa8a17f825e03a0 100644 (file)
--- 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 (file)
index 0000000..9e8c61e
--- /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]]