[llvm] 569ccfc - [SCEV] more accurate range for addrecexpr with nsw flag.

[Zheng Chen via llvm-commits]

Author: Zheng Chen
Date: 2020-01-11T23:26:35-05:00
New Revision: 569ccfc384a5434c35c09adba8c44c46014297e6

URL: https://github.com/llvm/llvm-project/commit/569ccfc384a5434c35c09adba8c44c46014297e6
DIFF: https://github.com/llvm/llvm-project/commit/569ccfc384a5434c35c09adba8c44c46014297e6.diff

LOG: [SCEV] more accurate range for addrecexpr with nsw flag.

Reviewed By: nikic

Differential Revision: https://reviews.llvm.org/D72436

Added: 
    

Modified: 
    llvm/lib/Analysis/ScalarEvolution.cpp
    llvm/test/Analysis/ScalarEvolution/range_nw_flag.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
index 7d5c71eafed6..f8d23c40e0c9 100644
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/lib/Analysis/ScalarEvolution.cpp
@@ -5678,23 +5678,31 @@ ScalarEvolution::getRangeRef(const SCEV *S,
           ConservativeResult = ConservativeResult.intersectWith(
               ConstantRange(C->getAPInt(), APInt(BitWidth, 0)), RangeType);
 
-    // If there's no signed wrap, and all the operands have the same sign or
-    // zero, the value won't ever change sign.
+    // If there's no signed wrap, and all the operands except initial value have
+    // the same sign or zero, the value won't ever be:
+    // 1: smaller than initial value if operands are non negative,
+    // 2: bigger than initial value if operands are non positive.
+    // For both cases, value can not cross signed min/max boundary.
     if (AddRec->hasNoSignedWrap()) {
       bool AllNonNeg = true;
       bool AllNonPos = true;
-      for (unsigned i = 0, e = AddRec->getNumOperands(); i != e; ++i) {
-        if (!isKnownNonNegative(AddRec->getOperand(i))) AllNonNeg = false;
-        if (!isKnownNonPositive(AddRec->getOperand(i))) AllNonPos = false;
+      for (unsigned i = 1, e = AddRec->getNumOperands(); i != e; ++i) {
+        if (!isKnownNonNegative(AddRec->getOperand(i)))
+          AllNonNeg = false;
+        if (!isKnownNonPositive(AddRec->getOperand(i)))
+          AllNonPos = false;
       }
       if (AllNonNeg)
         ConservativeResult = ConservativeResult.intersectWith(
-          ConstantRange(APInt(BitWidth, 0),
-                        APInt::getSignedMinValue(BitWidth)), RangeType);
+            ConstantRange::getNonEmpty(getSignedRangeMin(AddRec->getStart()),
+                                       APInt::getSignedMinValue(BitWidth)),
+            RangeType);
       else if (AllNonPos)
         ConservativeResult = ConservativeResult.intersectWith(
-          ConstantRange(APInt::getSignedMinValue(BitWidth),
-                        APInt(BitWidth, 1)), RangeType);
+            ConstantRange::getNonEmpty(
+                APInt::getSignedMinValue(BitWidth),
+                getSignedRangeMax(AddRec->getStart()) + 1),
+            RangeType);
     }
 
     // TODO: non-affine addrec

diff  --git a/llvm/test/Analysis/ScalarEvolution/range_nw_flag.ll b/llvm/test/Analysis/ScalarEvolution/range_nw_flag.ll
index 336a84472410..ae447dcdfa57 100644
--- a/llvm/test/Analysis/ScalarEvolution/range_nw_flag.ll
+++ b/llvm/test/Analysis/ScalarEvolution/range_nw_flag.ll
@@ -40,7 +40,7 @@ exit:
 }
 
 ; CHECK-LABEL: @test-addrec-nsw-start-neg-strip-neg
-; CHECK: -->  {(-1 + (-10 smin %offset))<nsw>,+,-1}<nsw><%loop> U: [-2147483648,1) S: [-2147483648,1)
+; CHECK: -->  {(-1 + (-10 smin %offset))<nsw>,+,-1}<nsw><%loop> U: [-2147483648,-10) S: [-2147483648,-10)
 define void @test-addrec-nsw-start-neg-strip-neg(float* %input, i32 %offset, i32 %numIterations) {
 entry:
   %cmp = icmp slt i32 %offset, -10
@@ -60,7 +60,7 @@ exit:
 }
 
 ; CHECK-LABEL: @test-addrec-nsw-start-pos-strip-neg
-; CHECK: -->  {(-1 + (10 smin %offset))<nsw>,+,-1}<nsw><%loop> U: full-set S: full-set
+; CHECK: -->  {(-1 + (10 smin %offset))<nsw>,+,-1}<nsw><%loop> U: [-2147483648,10) S: [-2147483648,10)
 define void @test-addrec-nsw-start-pos-strip-neg(float* %input, i32 %offset, i32 %numIterations) {
 entry:
   %cmp = icmp slt i32 %offset, 10
@@ -80,7 +80,7 @@ exit:
 }
 
 ; CHECK-LABEL: @test-addrec-nsw-start-pos-strip-pos
-; CHECK: -->  {(1 + (10 smax %offset))<nuw><nsw>,+,1}<nuw><nsw><%loop> U: [0,-2147483648) S: [0,-2147483648)
+; CHECK: -->  {(1 + (10 smax %offset))<nuw><nsw>,+,1}<nuw><nsw><%loop> U: [11,-2147483648) S: [11,-2147483648)
 define void @test-addrec-nsw-start-pos-strip-pos(float* %input, i32 %offset, i32 %numIterations) {
 entry:
   %cmp = icmp sgt i32 %offset, 10
@@ -100,7 +100,7 @@ exit:
 }
 
 ; CHECK-LABEL: @test-addrec-nsw-start-neg-strip-pos
-; CHECK: -->  {(1 + (-10 smax %offset))<nsw>,+,1}<nsw><%loop> U: full-set S: full-set
+; CHECK: -->  {(1 + (-10 smax %offset))<nsw>,+,1}<nsw><%loop> U: [-9,-2147483648) S: [-9,-2147483648)
 define void @test-addrec-nsw-start-neg-strip-pos(float* %input, i32 %offset, i32 %numIterations) {
 entry:
   %cmp = icmp sgt i32 %offset, -10