[Mlir-commits] [mlir] [MLIR][NVVM] Fix predicate operand index in BasicPtxBuilderInterface (PR #189552)
Guray Ozen
llvmlistbot at llvm.org
Tue Mar 31 03:32:47 PDT 2026
https://github.com/grypp updated https://github.com/llvm/llvm-project/pull/189552
>From bfa1d6bd01d32867dac874b9948ee154c56f1cc0 Mon Sep 17 00:00:00 2001
From: Guray Ozen <gozen at nvidia.com>
Date: Tue, 31 Mar 2026 12:11:51 +0200
Subject: [PATCH] [MLIR][NVVM] Fix predicate operand index in
BasicPtxBuilderInterface
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The predicate's @$N index was computed as ptxOperands.size() - 1, which
only counts input operands (Read + ReadWrite). LLVM inline asm numbers
outputs first then inputs, so when write-only outputs are present the
index is off by the number of output constraints.
Compute the correct index by finding the last non-tied token in the
canonicalized constraint string — tied digit-only tokens (from
read-write canonicalization) are appended at the end, and the predicate
"b" constraint immediately precedes them.
Also fix the existing ex2 predicate test which encoded the buggy @$1
(pointing to the f32 input) instead of the correct @$2 (the i1
predicate), and add new tests covering:
- write-only outputs + predicate (multi_return_pred)
- read-write + predicate with tied constraints (inline_ptx_multi_rw_pred)
- read-write + write-only + read + predicate (inline_ptx_multi_rw_r_pred)
Made-with: Cursor
---
.../LLVMIR/IR/BasicPtxBuilderInterface.cpp | 28 ++++++++-
.../Conversion/NVVMToLLVM/nvvm-to-llvm.mlir | 61 ++++++++++++++++++-
2 files changed, 87 insertions(+), 2 deletions(-)
diff --git a/mlir/lib/Dialect/LLVMIR/IR/BasicPtxBuilderInterface.cpp b/mlir/lib/Dialect/LLVMIR/IR/BasicPtxBuilderInterface.cpp
index d85b2ad9a0542..9ce413ceeaf6b 100644
--- a/mlir/lib/Dialect/LLVMIR/IR/BasicPtxBuilderInterface.cpp
+++ b/mlir/lib/Dialect/LLVMIR/IR/BasicPtxBuilderInterface.cpp
@@ -423,6 +423,31 @@ static std::string rewriteAsmPlaceholders(llvm::StringRef ptxCode) {
return out;
}
+/// Return the constraint index of the predicate operand. The predicate
+/// constraint ("b") is always the last non-tied token in the canonicalized
+/// constraint string. Tied constraints (digit-only tokens from read-write
+/// canonicalization) are appended at the end, so we walk backwards to skip
+/// them.
+static unsigned getPredicateConstraintIndex(StringRef constraints) {
+ SmallVector<StringRef> tokens;
+ constraints.split(tokens, ',');
+ assert(!tokens.empty() && "expected at least a predicate constraint");
+
+ auto isTiedConstraint = [](StringRef tok) {
+ unsigned idx;
+ return !tok.trim().getAsInteger(10, idx);
+ };
+
+ size_t numTied = 0;
+ for (StringRef tok : llvm::reverse(tokens)) {
+ if (!isTiedConstraint(tok))
+ break;
+ ++numTied;
+ }
+ assert(numTied < tokens.size() && "all constraints are tied");
+ return tokens.size() - numTied - 1;
+}
+
LLVM::InlineAsmOp PtxBuilder::build() {
auto asmDialectAttr = LLVM::AsmDialectAttr::get(interfaceOp->getContext(),
LLVM::AsmDialect::AD_ATT);
@@ -443,8 +468,9 @@ LLVM::InlineAsmOp PtxBuilder::build() {
// Add the predicate to the asm string.
if (interfaceOp.getPredicate().has_value() &&
interfaceOp.getPredicate().value()) {
+ unsigned predIdx = getPredicateConstraintIndex(registerConstraints);
std::string predicateStr = "@%";
- predicateStr += std::to_string((ptxOperands.size() - 1));
+ predicateStr += std::to_string(predIdx);
ptxInstruction = predicateStr + " " + ptxInstruction;
}
diff --git a/mlir/test/Conversion/NVVMToLLVM/nvvm-to-llvm.mlir b/mlir/test/Conversion/NVVMToLLVM/nvvm-to-llvm.mlir
index 8e16a92d96a7b..a188aec18134c 100644
--- a/mlir/test/Conversion/NVVMToLLVM/nvvm-to-llvm.mlir
+++ b/mlir/test/Conversion/NVVMToLLVM/nvvm-to-llvm.mlir
@@ -614,11 +614,25 @@ llvm.func @ex2(%input : f32, %pred : i1) {
// CHECK: %{{.*}} = llvm.inline_asm has_side_effects asm_dialect = att "ex2.approx.ftz.f32 $0, $1;", "=f,f" %{{.*}} : (f32) -> f32
%0 = nvvm.inline_ptx "ex2.approx.ftz.f32 {$w0}, {$r0};" ro (%input : f32) -> f32
- // CHECK: %{{.*}} = llvm.inline_asm has_side_effects asm_dialect = att "@$1 ex2.approx.ftz.f32 $0, $1;", "=f,f,b" %{{.*}}, %{{.*}} : (f32, i1) -> f32
+ // CHECK: %{{.*}} = llvm.inline_asm has_side_effects asm_dialect = att "@$2 ex2.approx.ftz.f32 $0, $1;", "=f,f,b" %{{.*}}, %{{.*}} : (f32, i1) -> f32
%1 = nvvm.inline_ptx "ex2.approx.ftz.f32 {$w0}, {$r0};" ro (%input : f32), predicate = %pred -> f32
llvm.return
}
+// CHECK-LABEL: @multi_return_pred(
+// CHECK-SAME: %[[arg0:[a-zA-Z0-9_]+]]: i32, %[[arg1:[a-zA-Z0-9_]+]]: i32, %[[pred:[a-zA-Z0-9_]+]]: i1)
+llvm.func @multi_return_pred(%a : i32, %b : i32, %pred : i1) -> i32 {
+ // CHECK: %[[S1:.+]] = llvm.inline_asm has_side_effects asm_dialect = att "@$4 {.reg .pred p; setp.ge.s32 p, $2, $3; selp.s32 $0, $2,$3, p; selp.s32 $1, $2,$3, p;}", "=r,=r,r,r,b" %[[arg0]], %[[arg1]], %[[pred]] : (i32, i32, i1) -> !llvm.struct<(i32, i32)>
+ // CHECK: %[[S2:.+]] = llvm.extractvalue %[[S1]][0] : !llvm.struct<(i32, i32)>
+ // CHECK: %[[S3:.+]] = llvm.extractvalue %[[S1]][1] : !llvm.struct<(i32, i32)>
+ // CHECK: %[[S4:.+]] = llvm.add %[[S2]], %[[S3]] : i32
+ // CHECK: llvm.return %[[S4]] : i32
+ %r1, %r2 = nvvm.inline_ptx "{.reg .pred p; setp.ge.s32 p, {$r0}, {$r1}; selp.s32 {$w0}, {$r0},{$r1}, p; selp.s32 {$w1}, {$r0},{$r1}, p;}"
+ ro (%a, %b : i32,i32), predicate = %pred -> i32,i32
+ %r3 = llvm.add %r1, %r2 : i32
+ llvm.return %r3 : i32
+}
+
// CHECK-LABEL: @multi_return(
// CHECK-SAME: %[[arg0:[a-zA-Z0-9_]+]]: i32, %[[arg1:[a-zA-Z0-9_]+]]: i32)
llvm.func @multi_return(%a : i32, %b : i32) -> i32 {
@@ -651,6 +665,24 @@ llvm.func @inline_ptx_multi_rw(%a : i32, %b : i32, %rw_c : f32, %rw_d : f32) ->
llvm.return %r4 : f32
}
+// CHECK-LABEL: @inline_ptx_multi_rw_pred(
+// CHECK-SAME: %[[arg0:[a-zA-Z0-9_]+]]: i32, %[[arg1:[a-zA-Z0-9_]+]]: i32, %[[arg2:[a-zA-Z0-9_]+]]: f32, %[[arg3:[a-zA-Z0-9_]+]]: f32, %[[pred:[a-zA-Z0-9_]+]]: i1)
+llvm.func @inline_ptx_multi_rw_pred(%a : i32, %b : i32, %rw_c : f32, %rw_d : f32, %pred : i1) -> f32 {
+// CHECK: %[[S0:.+]] = llvm.inline_asm has_side_effects asm_dialect = att "@$4 {.reg .pred p; setp.ge.s32 p, $2, $3; selp.s32 $0, $2,$3, p; selp.s32 $1, $2,$3, p;}",
+// CHECK-SAME: "=f,=f,r,r,b,0,1"
+// CHECK-SAME: %[[arg2]], %[[arg3]], %[[arg0]], %[[arg1]], %[[pred]]
+// CHECK-SAME: : (f32, f32, i32, i32, i1) -> !llvm.struct<(f32, f32)>
+// CHECK: %[[S1:.+]] = llvm.extractvalue %[[S0]][0] : !llvm.struct<(f32, f32)>
+// CHECK: %[[S2:.+]] = llvm.extractvalue %[[S0]][1] : !llvm.struct<(f32, f32)>
+// CHECK: %[[S3:.+]] = llvm.fadd %[[S1]], %[[S2]] : f32
+// CHECK: llvm.return %[[S3]] : f32
+ nvvm.inline_ptx "{.reg .pred p; setp.ge.s32 p, {$r0}, {$r1}; selp.s32 {$rw0}, {$r0},{$r1}, p; selp.s32 {$rw1}, {$r0},{$r1}, p;}"
+ ro (%a, %b : i32,i32)
+ rw (%rw_c, %rw_d: f32,f32), predicate = %pred
+ %r4 = llvm.fadd %rw_c, %rw_d : f32
+ llvm.return %r4 : f32
+}
+
// CHECK-LABEL: @inline_ptx_multi_rw_r(
// CHECK-SAME: %[[arg0:[a-zA-Z0-9_]+]]: i32, %[[arg1:[a-zA-Z0-9_]+]]: i32, %[[arg2:[a-zA-Z0-9_]+]]: f32, %[[arg3:[a-zA-Z0-9_]+]]: f32)
llvm.func @inline_ptx_multi_rw_r(%a : i32, %b : i32, %rw_c : f32, %rw_d : f32) -> f32 {
@@ -678,6 +710,33 @@ llvm.func @inline_ptx_multi_rw_r(%a : i32, %b : i32, %rw_c : f32, %rw_d : f32)
llvm.return %r5 : f32
}
+// CHECK-LABEL: @inline_ptx_multi_rw_r_pred(
+// CHECK-SAME: %[[arg0:[a-zA-Z0-9_]+]]: i32, %[[arg1:[a-zA-Z0-9_]+]]: i32, %[[arg2:[a-zA-Z0-9_]+]]: f32, %[[arg3:[a-zA-Z0-9_]+]]: f32, %[[pred:[a-zA-Z0-9_]+]]: i1)
+llvm.func @inline_ptx_multi_rw_r_pred(%a : i32, %b : i32, %rw_c : f32, %rw_d : f32, %pred : i1) -> f32 {
+// CHECK: %[[S0:.+]] = llvm.inline_asm has_side_effects asm_dialect = att "@$6 {.reg .pred p; setp.ge.s32 p, $4, $5; selp.s32 $0, $4,$5, p; selp.s32 $1, $4,$5, p; selp.s32 $2, $4,$5, p; selp.s32 $3, $4,$5, p;}",
+// CHECK-SAME: "=f,=f,=r,=r,r,r,b,0,1"
+// CHECK-SAME: %[[arg2]], %[[arg3]], %[[arg0]], %[[arg1]], %[[pred]] :
+// CHECK-SAME: (f32, f32, i32, i32, i1) -> !llvm.struct<(f32, f32, i32, i32)>
+// CHECK: %[[S1:.+]] = llvm.extractvalue %[[S0]][0] : !llvm.struct<(f32, f32, i32, i32)>
+// CHECK: %[[S2:.+]] = llvm.extractvalue %[[S0]][1] : !llvm.struct<(f32, f32, i32, i32)>
+// CHECK: %[[S3:.+]] = llvm.extractvalue %[[S0]][2] : !llvm.struct<(f32, f32, i32, i32)>
+// CHECK: %[[S4:.+]] = llvm.extractvalue %[[S0]][3] : !llvm.struct<(f32, f32, i32, i32)>
+// CHECK: %[[S5:.+]] = llvm.add %[[S3]], %[[S4]] : i32
+// CHECK: %[[S6:.+]] = llvm.sitofp %[[S5]] : i32 to f32
+// CHECK: %[[S7:.+]] = llvm.fadd %[[S1]], %[[S2]] : f32
+// CHECK: %[[S8:.+]] = llvm.fadd %[[S6]], %[[S2]] : f32
+// CHECK: llvm.return %[[S8]] : f32
+
+ %wo0, %wo1 = nvvm.inline_ptx "{.reg .pred p; setp.ge.s32 p, {$r0}, {$r1}; selp.s32 {$rw0}, {$r0},{$r1}, p; selp.s32 {$rw1}, {$r0},{$r1}, p; selp.s32 {$w0}, {$r0},{$r1}, p; selp.s32 {$w1}, {$r0},{$r1}, p;}"
+ ro (%a, %b : i32,i32)
+ rw (%rw_c, %rw_d: f32,f32), predicate = %pred -> i32,i32
+ %r3 = llvm.add %wo0, %wo1 : i32
+ %r3f = llvm.sitofp %r3 : i32 to f32
+ %r4 = llvm.fadd %rw_c, %rw_d : f32
+ %r5 = llvm.fadd %r3f, %rw_d : f32
+ llvm.return %r5 : f32
+}
+
// -----
llvm.func @inline_ptx_pack_4i8(%src : vector<4xi8>, %mask : i32, %zero: i32) {
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