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Renesas SH-4 Registers

9/7/2007

The Renesas SuperH SH-4 has 16 general-purpose registers. The following table shows the roles assigned to these registers.

Register Description

R0

Serves as a temporary register when expanding assembly language pseudo-instructions, and holds function return values.

In addition, R0 serves as an implicit source or destination in byte and 16-bit operations.

Not preserved.

R1-R3

Serve as temporary registers

Not preserved

R4-R7

Hold the first four words of integer and non-scalar incoming arguments. The argument build area provides space into which R4 through R7 holding arguments may spill.

Not preserved.

R8-R13

Serve as permanent registers

Preserved

R14

Serves as the default frame pointer. Any other permanent register may serve as the frame pointer, and leaf routines may use a temporary register as the frame pointer.

Preserved.

R15

Serves as the stack pointer or as a permanent register

Preserved.

The SH-4 has two banks of 16 floating-point registers designated Bank0 and Bank1. This specification does not define the use of Bank1. This calling convention assigns the following roles to the SH-4 Bank0 floating-point registers.

Double-Precision Register Single-Precision Register Description

DR0

FR0

FR1

Hold function return values. DR0 is another name for the single-precision registers FR0 and FR1 as a pair.

DR2

FR2-FR3

Serve as temporary registers. DR2 is another name for FR2 and FR3 as a pair.

Not preserved

DR4-DR10

FR4-FR11

Hold single- or double-precision floating-point arguments. The argument build area also provides space into which floating-point registers holding arguments may spill.

DR12-DR14

FR12-FR15

Serve as permanent registers.

Preserved

The floating-point status control affects the behavior of some floating-point instructions. For information about the use of the PR, SZ, and FR bits within prologs and epilogs, see Renesas SH-4 Prolog and Epilog.

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