[llvm] 0b46f19 - [Support] Ensure KnownBits::sextInReg can handle the src == dst sext-in-reg case.

[Simon Pilgrim via llvm-commits]

Author: Simon Pilgrim
Date: 2021-01-14T14:50:21Z
New Revision: 0b46f19a9ecd6215cffb51d19f2403c18b0226f5

URL: https://github.com/llvm/llvm-project/commit/0b46f19a9ecd6215cffb51d19f2403c18b0226f5
DIFF: https://github.com/llvm/llvm-project/commit/0b46f19a9ecd6215cffb51d19f2403c18b0226f5.diff

LOG: [Support] Ensure KnownBits::sextInReg can handle the src == dst sext-in-reg case.

This was resulting in assertions inside APInt::zext that we were extending to the same bitwidth.

Added: 
    

Modified: 
    llvm/lib/Support/KnownBits.cpp
    llvm/unittests/Support/KnownBitsTest.cpp

Removed: 
    


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diff  --git a/llvm/lib/Support/KnownBits.cpp b/llvm/lib/Support/KnownBits.cpp
index 0f36c6a9ef1d..a46a90bb97d4 100644
--- a/llvm/lib/Support/KnownBits.cpp
+++ b/llvm/lib/Support/KnownBits.cpp
@@ -85,7 +85,11 @@ KnownBits KnownBits::computeForAddSub(bool Add, bool NSW,
 
 KnownBits KnownBits::sextInReg(unsigned SrcBitWidth) const {
   unsigned BitWidth = getBitWidth();
-  assert(BitWidth >= SrcBitWidth && "Illegal sext-in-register");
+  assert(0 < SrcBitWidth && SrcBitWidth <= BitWidth &&
+         "Illegal sext-in-register");
+
+  if (SrcBitWidth == BitWidth)
+    return *this;
 
   // Sign extension.  Compute the demanded bits in the result that are not
   // present in the input.

diff  --git a/llvm/unittests/Support/KnownBitsTest.cpp b/llvm/unittests/Support/KnownBitsTest.cpp
index 991096098b8e..4e69df49837e 100644
--- a/llvm/unittests/Support/KnownBitsTest.cpp
+++ b/llvm/unittests/Support/KnownBitsTest.cpp
@@ -427,7 +427,7 @@ TEST(KnownBitsTest, SExtOrTrunc) {
 
 TEST(KnownBitsTest, SExtInReg) {
   unsigned Bits = 4;
-  for (unsigned FromBits = 1; FromBits != Bits; ++FromBits) {
+  for (unsigned FromBits = 1; FromBits <= Bits; ++FromBits) {
     ForeachKnownBits(Bits, [&](const KnownBits &Known) {
       APInt CommonOne = APInt::getAllOnesValue(Bits);
       APInt CommonZero = APInt::getAllOnesValue(Bits);