teach SCEV that the scale and addition of an inbounds gep don't NSW.

This fixes a FIXME in scev-aa.ll (allowing a new no-alias result) and
generally makes things more precise.

llvm-svn: 125449

llvm/lib/Analysis/ScalarEvolution.cpp

@@ -2870,6 +2870,7 @@ const SCEV *ScalarEvolution::createNodeForGEP(GEPOperator *GEP) {
   // Add expression, because the Instruction may be guarded by control flow
   // and the no-overflow bits may not be valid for the expression in any
   // context.
+  bool isInBounds = GEP->isInBounds();
 
   const Type *IntPtrTy = getEffectiveSCEVType(GEP->getType());
   Value *Base = GEP->getOperand(0);
@@ -2898,7 +2899,8 @@ const SCEV *ScalarEvolution::createNodeForGEP(GEPOperator *GEP) {
       IndexS = getTruncateOrSignExtend(IndexS, IntPtrTy);
 
       // Multiply the index by the element size to compute the element offset.
-      const SCEV *LocalOffset = getMulExpr(IndexS, ElementSize);
+      const SCEV *LocalOffset = getMulExpr(IndexS, ElementSize, /*NUW*/ false,
+                                           /*NSW*/ isInBounds);
 
       // Add the element offset to the running total offset.
       TotalOffset = getAddExpr(TotalOffset, LocalOffset);
@@ -2909,7 +2911,8 @@ const SCEV *ScalarEvolution::createNodeForGEP(GEPOperator *GEP) {
   const SCEV *BaseS = getSCEV(Base);
 
   // Add the total offset from all the GEP indices to the base.
-  return getAddExpr(BaseS, TotalOffset);
+  return getAddExpr(BaseS, TotalOffset, /*NUW*/ false,
+                    /*NSW*/ isInBounds);
 }
 
 /// GetMinTrailingZeros - Determine the minimum number of zero bits that S is

llvm/test/Analysis/ScalarEvolution/nsw.ll

@@ -76,3 +76,31 @@ for.cond.for.end_crit_edge.i.i:                   ; preds = %for.body.i.i
 _ZSt4fillIPiiEvT_S1_RKT0_.exit:                   ; preds = %entry, %for.cond.for.end_crit_edge.i.i
   ret void
 }
+
+; Various checks for inbounds geps.
+define void @test3(i32* %begin, i32* %end) nounwind ssp {
+entry:
+  %cmp7.i.i = icmp eq i32* %begin, %end
+  br i1 %cmp7.i.i, label %_ZSt4fillIPiiEvT_S1_RKT0_.exit, label %for.body.i.i
+
+for.body.i.i:                                     ; preds = %entry, %for.body.i.i
+  %indvar.i.i = phi i64 [ %tmp, %for.body.i.i ], [ 0, %entry ]
+; CHECK: %indvar.i.i
+; CHECK: {0,+,1}<nuw><nsw><%for.body.i.i>
+  %tmp = add nsw i64 %indvar.i.i, 1
+; CHECK: %tmp = 
+; CHECK: {1,+,1}<nuw><nsw><%for.body.i.i>
+  %ptrincdec.i.i = getelementptr inbounds i32* %begin, i64 %tmp
+; CHECK: %ptrincdec.i.i =
+; CHECK: {(4 + %begin),+,4}<nsw><%for.body.i.i>
+  %__first.addr.08.i.i = getelementptr inbounds i32* %begin, i64 %indvar.i.i
+; CHECK: %__first.addr.08.i.i
+; CHECK: {%begin,+,4}<nsw><%for.body.i.i>
+  store i32 0, i32* %__first.addr.08.i.i, align 4
+  %cmp.i.i = icmp eq i32* %ptrincdec.i.i, %end
+  br i1 %cmp.i.i, label %_ZSt4fillIPiiEvT_S1_RKT0_.exit, label %for.body.i.i
+; CHECK: Loop %for.body.i.i: Unpredictable backedge-taken count. 
+; CHECK: Loop %for.body.i.i: Unpredictable max backedge-taken count.
+_ZSt4fillIPiiEvT_S1_RKT0_.exit:                   ; preds = %for.body.i.i, %entry
+  ret void
+}

llvm/test/Analysis/ScalarEvolution/scev-aa.ll

@@ -190,9 +190,8 @@ define void @bar() {
   ret void
 }
 
-; TODO: This is theoretically provable to be NoAlias.
 ; CHECK: Function: nonnegative: 2 pointers, 0 call sites
-; CHECK: MayAlias:  i64* %arrayidx, i64* %p
+; CHECK: NoAlias:  i64* %arrayidx, i64* %p
 
 define void @nonnegative(i64* %p) nounwind {
 entry:
@@ -211,6 +210,6 @@ for.end:                                          ; preds = %for.body, %entry
   ret void
 }
 
-; CHECK: 13 no alias responses
+; CHECK: 14 no alias responses
-; CHECK: 27 may alias responses
+; CHECK: 26 may alias responses
 ; CHECK: 18 must alias responses