[SCCP] Don't violate the lattice invariants

We marked values which are 'undef' as constant instead of undefined
which violates SCCP's invariants.  If we can figure out that a
computation results in 'undef', leave it in the undefined state.

This fixes PR16052.

llvm-svn: 257102

lib/Transforms/Scalar/SCCP.cpp

@@ -757,9 +757,14 @@ void SCCPSolver::visitCastInst(CastInst &I) {
   LatticeVal OpSt = getValueState(I.getOperand(0));
   if (OpSt.isOverdefined())          // Inherit overdefinedness of operand
     markOverdefined(&I);
-  else if (OpSt.isConstant())        // Propagate constant value
+  else if (OpSt.isConstant()) {
-    markConstant(&I, ConstantExpr::getCast(I.getOpcode(),
+    Constant *C =
-                                           OpSt.getConstant(), I.getType()));
+        ConstantExpr::getCast(I.getOpcode(), OpSt.getConstant(), I.getType());
+    if (isa<UndefValue>(C))
+      return;
+    // Propagate constant value
+    markConstant(&I, C);
+  }
 }
 
 
@@ -859,10 +864,14 @@ void SCCPSolver::visitBinaryOperator(Instruction &I) {
   LatticeVal &IV = ValueState[&I];
   if (IV.isOverdefined()) return;
 
-  if (V1State.isConstant() && V2State.isConstant())
+  if (V1State.isConstant() && V2State.isConstant()) {
-    return markConstant(IV, &I,
+    Constant *C = ConstantExpr::get(I.getOpcode(), V1State.getConstant(),
-                        ConstantExpr::get(I.getOpcode(), V1State.getConstant(),
+                                    V2State.getConstant());
-                                          V2State.getConstant()));
+    // X op Y -> undef.
+    if (isa<UndefValue>(C))
+      return;
+    return markConstant(IV, &I, C);
+  }
 
   // If something is undef, wait for it to resolve.
   if (!V1State.isOverdefined() && !V2State.isOverdefined())
@@ -917,10 +926,13 @@ void SCCPSolver::visitCmpInst(CmpInst &I) {
   LatticeVal &IV = ValueState[&I];
   if (IV.isOverdefined()) return;
 
-  if (V1State.isConstant() && V2State.isConstant())
+  if (V1State.isConstant() && V2State.isConstant()) {
-    return markConstant(IV, &I, ConstantExpr::getCompare(I.getPredicate(),
+    Constant *C = ConstantExpr::getCompare(
-                                                         V1State.getConstant(),
+        I.getPredicate(), V1State.getConstant(), V2State.getConstant());
-                                                        V2State.getConstant()));
+    if (isa<UndefValue>(C))
+      return;
+    return markConstant(IV, &I, C);
+  }
 
   // If operands are still undefined, wait for it to resolve.
   if (!V1State.isOverdefined() && !V2State.isOverdefined())
@@ -1020,8 +1032,11 @@ void SCCPSolver::visitGetElementPtrInst(GetElementPtrInst &I) {
 
   Constant *Ptr = Operands[0];
   auto Indices = makeArrayRef(Operands.begin() + 1, Operands.end());
-  markConstant(&I, ConstantExpr::getGetElementPtr(I.getSourceElementType(), Ptr,
+  Constant *C =
-                                                  Indices));
+      ConstantExpr::getGetElementPtr(I.getSourceElementType(), Ptr, Indices);
+  if (isa<UndefValue>(C))
+      return;
+  markConstant(&I, C);
 }
 
 void SCCPSolver::visitStoreInst(StoreInst &SI) {
@@ -1079,8 +1094,11 @@ void SCCPSolver::visitLoadInst(LoadInst &I) {
   }
 
   // Transform load from a constant into a constant if possible.
-  if (Constant *C = ConstantFoldLoadFromConstPtr(Ptr, DL))
+  if (Constant *C = ConstantFoldLoadFromConstPtr(Ptr, DL)) {
+    if (isa<UndefValue>(C))
+      return;
     return markConstant(IV, &I, C);
+  }
 
   // Otherwise we cannot say for certain what value this load will produce.
   // Bail out.
@@ -1122,8 +1140,12 @@ CallOverdefined:
 
       // If we can constant fold this, mark the result of the call as a
       // constant.
-      if (Constant *C = ConstantFoldCall(F, Operands, TLI))
+      if (Constant *C = ConstantFoldCall(F, Operands, TLI)) {
+        // call -> undef.
+        if (isa<UndefValue>(C))
+          return;
         return markConstant(I, C);
+      }
     }
 
     // Otherwise, we don't know anything about this call, mark it overdefined.
@@ -1379,6 +1401,11 @@ bool SCCPSolver::ResolvedUndefsIn(Function &F) {
         // X % undef -> undef.  No change.
         if (Op1LV.isUndefined()) break;
 
+        // X / 0 -> undef.  No change.
+        // X % 0 -> undef.  No change.
+        if (Op1LV.isConstant() && Op1LV.getConstant()->isZeroValue())
+          break;
+
         // undef / X -> 0.   X could be maxint.
         // undef % X -> 0.   X could be 1.
         markForcedConstant(&I, Constant::getNullValue(ITy));

test/Transforms/IPConstantProp/PR16052.ll

@@ -0,0 +1,26 @@
+; 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 i64 @fn2() {
+entry:
+  %conv = sext i32 undef to i64
+  %div = sdiv i64 8, %conv
+  %call2 = call i64 @fn1(i64 %div)
+  ret i64 %call2
+}
+
+; CHECK-DAG: define i64 @fn2(
+; CHECK: %[[CALL:.*]] = call i64 @fn1(i64 undef)
+
+define internal i64 @fn1(i64 %p1) {
+entry:
+  %tobool = icmp ne i64 %p1, 0
+  %cond = select i1 %tobool, i64 %p1, i64 %p1
+  ret i64 %cond
+}
+
+; CHECK-DAG: define internal i64 @fn1(
+; CHECK: %[[SEL:.*]] = select i1 undef, i64 undef, i64 undef
+; CHECK: ret i64 %[[SEL]]