Do not approximate erf on rocm. (#19969)

On ROCm, we want to use the device library functions, which we link as
bitcode and inline. In this PR, we start with `math.erf` because that's
the immediate use case, but this will likely be generalized to other
functions in a subsequent PR.

Signed-off-by: Benoit Jacob <[email protected]>

Author: bjacob

compiler/src/iree/compiler/Codegen/Common/MathTransformPass.cpp

@@ -99,7 +99,6 @@ static bool predicateF32Cast(StringRef name,
 
 static bool predicateApprox(StringRef name,
                             IREE::HAL::ExecutableTargetAttr target) {
-  (void)target;                // Currently unused.
   if (clNativeMathPrecision) { // Legacy.
     if (name == math::ErfOp::getOperationName()) {
       // The legacy implementation had a bug: it always applied polynomial
@@ -124,6 +123,9 @@ static bool predicateApprox(StringRef name,
   StringRef expm1 = math::ExpM1Op::getOperationName();
   StringRef cbrt = math::CbrtOp::getOperationName();
   StringRef erf = math::ErfOp::getOperationName();
+  if (isROCMBackend(target) && name == erf) {
+    return false;
+  }
   return llvm::is_contained({atan, atan2, tanh, log, log2, log1p, erf, asin,
                              acos, exp, expm1, cbrt, sin, cos},
                             name);

compiler/src/iree/compiler/Codegen/Common/test/math_transform.mlir

@@ -55,3 +55,20 @@ func.func @rewrite_erf(%arg0: f16) -> f16 attributes {
   %0 = math.erf %arg0 : f16
   return %0 : f16
 }
+
+// -----
+
+// CHECK-LABEL: @no_approx_erf_on_rocm
+func.func @no_approx_erf_on_rocm(%arg0: f16) -> f16 attributes {
+  hal.executable.target =  #hal.executable.target<"rocm", "rocm-hsaco-fb", {}>
+} {
+  // On ROCm, we want to use the native device library function, so math.erf
+  // should not get rewritten. It's OK for f16 to still get casted to f32, as
+  // the device library function for f16 is casting to f32 anyway.
+  // CHECK:         math.erf
+  // CHECK-NOT:     math.exp
+  // CHECK-NOT:     math.log
+  // CHECK-NOT:     math.fma
+  %0 = math.erf %arg0 : f16
+  return %0 : f16
+}