error: couldn't allocate input reg for constraint 'r' on MIPS when building some wasm2c-generated code

[glandium]

This is similar to #52638, but for floats.

Reduced C reproducer:

float a;
void foo() {
    __asm__("" :: "r"(a));
}

$ clang --target=mips64el-linux-gnuabi64 -c test.c
test.c:3:13: error: couldn't allocate input reg for constraint 'r'
    __asm__("" :: "r"(a));
            ^
1 error generated.

Reduced LLVM IR reproducer:

target triple = "mips64el-unknown-linux-gnuabi64"

define void @foo() {
  call void asm sideeffect "", "r,~{$1}"(float 0.000000e+00)
  ret void
}

$ llc test.ll
error: couldn't allocate input reg for constraint 'r'

[llvmbot]

@llvm/issue-subscribers-backend-mips

[glandium]

(yes, technically, the r constraint is wrong because r is supposed to be for GPRs, but GCC is happy with this)