AMDGPU: Fix packed 16-bit inline constants (#76522)

Consistently treat packed 16-bit operands as 32-bit values, because
that's really what they are. The attempt to treat them differently was
ultimately incorrect and lead to miscompiles, e.g. when using non-splat
constants such as (1, 0) as operands.

Recognize 32-bit float constants for i/u16 instructions. This is a bit
odd conceptually, but it matches HW behavior and SP3.

Remove isFoldableLiteralV216; there was too much magic in the dependency
between it and its use in SIFoldOperands. Instead, we now simply rely on
checking whether a constant is an inline constant, and trying a bunch of
permutations of the low and high halves. This is more obviously correct
and leads to some new cases where inline constants are used as shown by
tests.

Move the logic for switching packed add vs. sub into SIFoldOperands.
This has two benefits: all logic that optimizes for inline constants in
packed math is now in one place; and it applies to both SelectionDAG and
GISel paths.

Disable the use of opsel with v_dot* instructions on gfx11. They are
documented to ignore opsel on src0 and src1. It may be interesting to
re-enable to use of opsel on src2 as a future optimization.

A similar "proper" fix of what inline constants mean could potentially
be applied to unpacked 16-bit ops. However, it's less clear what the
benefit would be, and there are surely places where we'd have to
carefully audit whether values are properly sign- or zero-extended. It
is best to keep such a change separate.

Fixes: Corruption in FSR 2.0 (latent bug exposed by an LLPC change)

1 files changed, 7 insertions, 4 deletions

diff --git a/llvm/lib/Target/AMDGPU/Utils/AMDGPUBaseInfo.h b/llvm/lib/Target/AMDGPU/Utils/AMDGPUBaseInfo.h
index 3c9f330..50c7417 100644
--- a/llvm/lib/Target/AMDGPU/Utils/AMDGPUBaseInfo.h
+++ b/llvm/lib/Target/AMDGPU/Utils/AMDGPUBaseInfo.h
@@ -1291,16 +1291,19 @@ LLVM_READNONE
 bool isInlinableLiteral16(int16_t Literal, bool HasInv2Pi);
 
 LLVM_READNONE
-bool isInlinableLiteralV216(int32_t Literal, bool HasInv2Pi);
+std::optional<unsigned> getInlineEncodingV2I16(uint32_t Literal);
 
 LLVM_READNONE
-bool isInlinableIntLiteralV216(int32_t Literal);
+std::optional<unsigned> getInlineEncodingV2F16(uint32_t Literal);
 
 LLVM_READNONE
-bool isInlinableLiteralV216(int32_t Literal, bool HasInv2Pi, uint8_t OpType);
+bool isInlinableLiteralV216(uint32_t Literal, uint8_t OpType);
 
 LLVM_READNONE
-bool isFoldableLiteralV216(int32_t Literal, bool HasInv2Pi);
+bool isInlinableLiteralV2I16(uint32_t Literal);
+
+LLVM_READNONE
+bool isInlinableLiteralV2F16(uint32_t Literal);
 
 LLVM_READNONE
 bool isValid32BitLiteral(uint64_t Val, bool IsFP64);