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[SPIR-V] Support printing OpConstantF literals wider than 64 bits #208219

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[SPIR-V] Support printing OpConstantF literals wider than 64 bits #208219

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[SPIR-V] Support printing OpConstantF literals wider than 64 bits
aobolensk Jul 8, 2026
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aobolensk Jul 8, 2026
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18 changes: 18 additions & 0 deletions llvm/lib/Target/SPIRV/MCTargetDesc/SPIRVInstPrinter.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -14,6 +14,7 @@
#include "SPIRV.h"
#include "SPIRVBaseInfo.h"
#include "llvm/ADT/APFloat.h"
#include "llvm/ADT/SmallString.h"
#include "llvm/MC/MCAsmInfo.h"
#include "llvm/MC/MCExpr.h"
#include "llvm/MC/MCInst.h"
Expand Down Expand Up @@ -70,6 +71,23 @@ void SPIRVInstPrinter::printOpConstantVarOps(const MCInst *MI,
return;
}

if (MI->getOpcode() == SPIRV::OpConstantF && NumVarOps > 2) {

@jmmartinez jmmartinez Jul 8, 2026

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I think you can just check for NumVarOps == 4. Any other case will hit the assert(TotalBits == 128 && "Unsupported floating-point literal width"); anyways.

@aobolensk aobolensk Jul 8, 2026

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Yes, thanks, done

// Wide floating-point literals (e.g. fp128) are encoded via more than two
// 32-bit words. Reconstruct the value and print it exactly.
const unsigned TotalBits = NumVarOps * 32;
APInt Val(TotalBits, 0);
for (unsigned I = 0; I < NumVarOps; ++I) {
uint64_t Word = MI->getOperand(StartIndex + I).getImm();
Val |= APInt(TotalBits, Word) << (I * 32);
}
assert(TotalBits == 128 && "Unsupported floating-point literal width");
APFloat FP(APFloat::IEEEquad(), Val);
SmallString<40> Str;
FP.toString(Str);
O << ' ' << Str;
return;
}

assert((NumVarOps == 1 || NumVarOps == 2) &&
"Unsupported number of bits for literal variable");

Expand Down
29 changes: 29 additions & 0 deletions llvm/test/CodeGen/SPIRV/constant/wide-float-literal-printer.mir
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@@ -0,0 +1,29 @@
# RUN: llc -O0 -mtriple=spirv32-unknown-unknown -start-after=finalize-isel -verify-machineinstrs %s -o - | FileCheck %s

# Exercises the SPIRVInstPrinter's OpConstantF path for literals wider than
# 64 bits (e.g. fp128), independent of how the OpConstantF instruction with
# more than two literal words was produced.

--- |
define fp128 @getConstantFP128() {
ret fp128 0xL00000000000000004001000000000000
}
Comment on lines +8 to +10

@jmmartinez jmmartinez Jul 8, 2026

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Why not write the test starting from the IR instead of the MIR ?

@aobolensk aobolensk Jul 8, 2026

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Unfortunately, there is another issue: there is a miscompilation of fp128 constant literals. I decided to split them gotta be done in the following patch

@aobolensk aobolensk Jul 8, 2026

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You may peek here: 0e27cc3

...
---
name: getConstantFP128
legalized: true
regBankSelected: true
selected: true
tracksRegLiveness: true
body: |
bb.1 (%ir-block.0):
%0:type = OpTypeFloat 128
%1:fid = OpConstantF %0, 0, 0, 0, 1073807360
%2:type = OpTypeFunction %0, %0
%3:iid = OpFunction %0, 0, %2
OpFunctionEnd
OpReturnValue %1

# CHECK: %[[#FP128:]] = OpTypeFloat 128
# CHECK: %[[#CST_FP128:]] = OpConstant %[[#FP128]] 4
# CHECK: OpReturnValue %[[#CST_FP128]]
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