Fix the sign-extending issue in right shift (#3820)

Fix issue  (#3637).

In constant folding of a right shift operation,slang always uses
signed interger as the operand no matter the input source code is
signed or unsigned, this could causes sign-extending issue if the
input source is unsigned integer with highest bit set to 1.

Fix the issue by checking the original type of the input and use
the unsigned type if the input is unsigned.

1 files changed, 26 insertions, 0 deletions

diff --git a/tests/bugs/gh-3637.slang b/tests/bugs/gh-3637.slang
new file mode 100644
index 000000000..81aa58c73
--- /dev/null
+++ b/tests/bugs/gh-3637.slang
@@ -0,0 +1,26 @@
+//TEST(compute):COMPARE_COMPUTE_EX(filecheck-buffer=CHECK):-cuda -compute -output-using-type
+//TEST(compute, vulkan):COMPARE_COMPUTE_EX(filecheck-buffer=CHECK):-vk -compute -output-using-type
+//TEST(compute):COMPARE_COMPUTE_EX(filecheck-buffer=CHECK):-cpu -compute -output-using-type
+
+// CHECK: 9223372036854775808
+// CHECK: 1
+// CHECK: 18446744073709551615
+
+// This tests exhibits a bug in constant folding in which the right shift
+// operator unconditionally performs sign-extension.
+
+//TEST_INPUT:ubuffer(data=[0 0 0 0 0 0 0 0], stride=8):out,name=outputBuffer
+RWStructuredBuffer<uint64_t> outputBuffer;
+
+[numthreads(1, 1, 1)]
+void computeMain(uint3 dispatchThreadID : SV_DispatchThreadID)
+{
+    const uint64_t topBitSet = 0x8000000000000000ull;
+    const uint64_t bottomBitSet = topBitSet >> 63;
+    const uint64_t allBitsSet = int64_t(topBitSet) >> 63; // expect sign-extending which will set all bits.
+    const uint64_t noBitsSet = topBitSet >> 64; // This exhibits undefined behaviour, as the compiler shifts right by at least the number of bits in the first operand
+    outputBuffer[0] = topBitSet;
+    outputBuffer[1] = bottomBitSet;
+    outputBuffer[2] = allBitsSet;
+    outputBuffer[3] = noBitsSet;
+}